path: root/ast/specmap.c

/*
*class++
*  Name:
*     SpecMap

*  Purpose:
*     Sequence of spectral coordinate conversions.

*  Constructor Function:
c     astSpecMap (also see astSpecAdd)
f     AST_SPECMAP (also see AST_SPECADD)

*  Description:
*     A SpecMap is a specialised form of Mapping which can be used to
*     represent a sequence of conversions between standard spectral
*     coordinate systems.
*
*     When an SpecMap is first created, it simply performs a unit
c     (null) Mapping. Using the astSpecAdd
f     (null) Mapping. Using the AST_SPECADD
c     function, a series of coordinate conversion steps may then be
f     routine, a series of coordinate conversion steps may then be
*     added. This allows multi-step conversions between a variety of
*     spectral coordinate systems to be assembled out of a set of building
*     blocks.
*
*     Conversions are available to transform between standards of rest.
*     Such conversions need to know the source position as an RA and DEC.
*     This information can be supplied in the form of parameters for
*     the relevant conversions, in which case the SpecMap is 1-dimensional,
*     simply transforming the spectral axis values. This means that the
*     same source position will always be used by the SpecMap. However, this
*     may not be appropriate for an accurate description of a 3-D spectral
*     cube, where changes of spatial position can produce significant
*     changes in the Doppler shift introduced when transforming between
*     standards of rest. For this situation, a 3-dimensional SpecMap can
*     be created in which axes 2 and 3 correspond to the source RA and DEC
*     The SpecMap simply copies values for axes 2 and 3 from input to
*     output), but modifies axis 1 values (the spectral axis) appropriately.
*
*     For details of the individual coordinate conversions available,
c     see the description of the astSpecAdd function.
f     see the description of the AST_SPECADD routine.

*  Inheritance:
*     The SpecMap class inherits from the Mapping class.

*  Attributes:
*     The SpecMap class does not define any new attributes beyond those
*     which are applicable to all Mappings.

*  Functions:
c     In addition to those functions applicable to all Mappings, the
c     following function may also be applied to all SpecMaps:
f     In addition to those routines applicable to all Mappings, the
f     following routine may also be applied to all SpecMaps:
*
c     - astSpecAdd: Add a spectral coordinate conversion to an SpecMap
f     - AST_SPECADD: Add a spectral coordinate conversion to an SpecMap

*  Copyright:
*     Copyright (C) 1997-2006 Council for the Central Laboratory of the
*     Research Councils
*     Copyright (C) 2009 Science & Technology Facilities Council.
*     All Rights Reserved.

*  Licence:
*     This program is free software: you can redistribute it and/or
*     modify it under the terms of the GNU Lesser General Public
*     License as published by the Free Software Foundation, either
*     version 3 of the License, or (at your option) any later
*     version.
*
*     This program is distributed in the hope that it will be useful,
*     but WITHOUT ANY WARRANTY; without even the implied warranty of
*     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*     GNU Lesser General Public License for more details.
*
*     You should have received a copy of the GNU Lesser General
*     License along with this program.  If not, see
*     <http://www.gnu.org/licenses/>.

*  Authors:
*     DSB: David S. Berry (Starlink)

*  History:
*     6-NOV-2002 (DSB):
*        Original version.
*     14-JUL-2003 (DSB):
*        Added checks for NAN values produced by transformation functions.
*     17-SEP-2003 (DSB):
*        - Improve FRTOAW accuracy by iterating.
*        - Changed Refrac to use algorithm given in FITS-WCS paper 3
*        version dated 21/9/03.
*     14-FEB-2006 (DSB):
*        Override astGetObjSize.
*     10-MAY-2006 (DSB):
*        Override astEqual.
*     15-NOV-2006 (DSB):
*        Guard against division by zero when converting freq to wave in
*        SystemChange.
*     18-JUN-2009 (DSB):
*        Add OBSALT argument to TPF2HL and HLF2TP conversions.
*        Change GEOLON/LAT to OBSLON/LAT for consistency with other
*        classes.
*     2-OCT-2012 (DSB):
*        Check for Infs as well as NaNs.
*     1-DEC-2016 (DSB):
*        Added a "narg" argumeent to astSpecAdd.

*class--
*/

/* Module Macros. */
/* ============== */
/* Set the name of the class we are implementing. This indicates to
   the header files that define class interfaces that they should make
   "protected" symbols available. */
#define astCLASS SpecMap

/* Codes to identify spectral coordinate conversions. */
#define AST__SPEC_NULL   0       /* Null value */
#define AST__FRTOVL      1       /* Frequency to relativistic velocity */
#define AST__VLTOFR      2       /* Relativistic velocity to Frequency */
#define AST__ENTOFR      3       /* Energy to frequency */
#define AST__FRTOEN      4       /* Frequency to energy */
#define AST__WNTOFR      5       /* Wave number to frequency */
#define AST__FRTOWN      6       /* Frequency to wave number */
#define AST__WVTOFR      7       /* Wavelength (vacuum) to frequency */
#define AST__FRTOWV      8       /* Frequency to wavelength (vacuum) */
#define AST__AWTOFR      9       /* Wavelength (air) to frequency */
#define AST__FRTOAW     10       /* Frequency to wavelength (air) */
#define AST__VRTOVL     11       /* Radio to relativistic velocity */
#define AST__VLTOVR     12       /* Relativistic to radio velocity */
#define AST__VOTOVL     13       /* Optical to relativistic velocity */
#define AST__VLTOVO     14       /* Relativistic to optical velocity */
#define AST__ZOTOVL     15       /* Redshift to relativistic velocity */
#define AST__VLTOZO     16       /* Relativistic velocity to redshift */
#define AST__BTTOVL     17       /* Beta factor to relativistic velocity */
#define AST__VLTOBT     18       /* Relativistic velocity to beta factor */
#define AST__USF2HL     19       /* User-defined to heliocentric frequency  */
#define AST__HLF2US     20       /* Heliocentric to user-defined frequency */
#define AST__TPF2HL     21       /* Topocentric to heliocentric frequency  */
#define AST__HLF2TP     22       /* Heliocentric to topocentric frequency */
#define AST__GEF2HL     23       /* Geocentric to heliocentric frequency */
#define AST__HLF2GE     24       /* Heliocentric to geocentric frequency */
#define AST__BYF2HL     25       /* Barycentric to heliocentric frequency */
#define AST__HLF2BY     26       /* Heliocentric to barycentric frequency */
#define AST__LKF2HL     27       /* LSRK to heliocentric frequency */
#define AST__HLF2LK     28       /* Heliocentric to LSRK frequency */
#define AST__LDF2HL     29       /* LSRD to heliocentric frequency */
#define AST__HLF2LD     30       /* Heliocentric to LSRD frequency */
#define AST__LGF2HL     31       /* Local group to heliocentric frequency */
#define AST__HLF2LG     32       /* Heliocentric to local group frequency */
#define AST__GLF2HL     33       /* Galactic to heliocentric frequency */
#define AST__HLF2GL     34       /* Heliocentric to galactic frequency */

/* Maximum number of arguments required by a conversion. */
#define MAX_ARGS 7

/* The alphabet (used for generating keywords for arguments). */
#define ALPHABET "abcdefghijklmnopqrstuvwxyz"

/* Angle conversion */
#define PI 3.141592653589793238462643
#define PIBY2 (PI/2.0)
#define D2R (PI/180.0)
#define R2D (180.0/PI)

/* Include files. */
/* ============== */
/* Interface definitions. */
/* ---------------------- */
#include "pal.h"              /* SLALIB interface */

#include "globals.h"             /* Thread-safe global data access */
#include "error.h"               /* Error reporting facilities */
#include "memory.h"              /* Memory allocation facilities */
#include "object.h"              /* Base Object class */
#include "pointset.h"            /* Sets of points/coordinates */
#include "mapping.h"             /* Coordinate Mappings (parent class) */
#include "unitmap.h"             /* Unit (null) Mappings */
#include "specmap.h"             /* Interface definition for this class */

/* Error code definitions. */
/* ----------------------- */
#include "ast_err.h"             /* AST error codes */

/* C header files. */
/* --------------- */
#include <ctype.h>
#include <stddef.h>
#include <stdio.h>
#include <string.h>
#include <math.h>

/* Module Variables. */
/* ================= */

/* Address of this static variable is used as a unique identifier for
   member of this class. */
static int class_check;

/* Pointers to parent class methods which are extended by this class. */
static int (* parent_getobjsize)( AstObject *, int * );
static AstPointSet *(* parent_transform)( AstMapping *, AstPointSet *, int, AstPointSet *, int * );
static double (* parent_rate)( AstMapping *, double *, int, int, int * );


#ifdef THREAD_SAFE
/* Define how to initialise thread-specific globals. */
#define GLOBAL_inits \
   globals->Class_Init = 0;

/* Create the function that initialises global data for this module. */
astMAKE_INITGLOBALS(SpecMap)

/* Define macros for accessing each item of thread specific global data. */
#define class_init astGLOBAL(SpecMap,Class_Init)
#define class_vtab astGLOBAL(SpecMap,Class_Vtab)


#include <pthread.h>


#else


/* Define the class virtual function table and its initialisation flag
   as static variables. */
static AstSpecMapVtab class_vtab;   /* Virtual function table */
static int class_init = 0;       /* Virtual function table initialised? */

#endif

/* Structure to hold parameters and intermediate values describing a
   reference frame */
typedef struct FrameDef {
   double obsalt;     /* Observers geodetic altitude (m) */
   double obslat;     /* Observers geodetic latitude (rads) */
   double obslon;     /* Observers geodetic longitude (rads, +ve east) */
   double epoch;      /* Julian epoch of observation */
   double refdec;     /* RA of reference point (FK5 J2000) */
   double refra;      /* DEC of reference point (FK5 J2000) */
   double veluser;    /* Heliocentric velocity of user-defined system (m/s) */
   double last;       /* Local apparent sideral time */
   double amprms[21]; /* Mean to apparent parameters */
   double vuser[3];   /* Used-defined velocity as a FK5 J2000 vector */
   double dvh[3];     /* Earth-sun velocity */
   double dvb[3];     /* Barycentre-sun velocity */
} FrameDef;

/* External Interface Function Prototypes. */
/* ======================================= */
/* The following functions have public prototypes only (i.e. no
   protected prototypes), so we must provide local prototypes for use
   within this module. */
AstSpecMap *astSpecMapId_( int, int, const char *, ... );

/* Prototypes for Private Member Functions. */
/* ======================================== */
static AstPointSet *Transform( AstMapping *, AstPointSet *, int, AstPointSet *, int * );
static const char *CvtString( int, const char **, int *, int *, int *, int *, const char *[ MAX_ARGS ], int * );
static double BaryVel( double, double, FrameDef *, int * );
static double GalVel( double, double, FrameDef *, int * );
static double GeoVel( double, double, FrameDef *, int * );
static double LgVel( double, double, FrameDef *, int * );
static double LsrdVel( double, double, FrameDef *, int * );
static double LsrkVel( double, double, FrameDef *, int * );
static double Rate( AstMapping *, double *, int, int, int * );
static double Refrac( double, int * );
static double Rverot( double, double, double, double, double, int * );
static double TopoVel( double, double, FrameDef *, int * );
static double UserVel( double, double, FrameDef *, int * );
static int CvtCode( const char *, int * );
static int Equal( AstObject *, AstObject *, int * );
static int FrameChange( int, int, double *, double *, double *, double *, int, int * );
static int MapMerge( AstMapping *, int, int, int *, AstMapping ***, int **, int * );
static int SystemChange( int, int, double *, double *, int, int * );
static void AddSpecCvt( AstSpecMap *, int, int, const double *, int * );
static void Copy( const AstObject *, AstObject *, int * );
static void Delete( AstObject *, int * );
static void Dump( AstObject *, AstChannel *, int * );
static void SpecAdd( AstSpecMap *, const char *, int, const double[], int * );

static int GetObjSize( AstObject *, int * );
/* Member functions. */
/* ================= */
static int Equal( AstObject *this_object, AstObject *that_object, int *status ) {
/*
*  Name:
*     Equal

*  Purpose:
*     Test if two SpecMaps are equivalent.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     int Equal( AstObject *this, AstObject *that, int *status )

*  Class Membership:
*     SpecMap member function (over-rides the astEqual protected
*     method inherited from the astMapping class).

*  Description:
*     This function returns a boolean result (0 or 1) to indicate whether
*     two SpecMaps are equivalent.

*  Parameters:
*     this
*        Pointer to the first Object (a SpecMap).
*     that
*        Pointer to the second Object.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     One if the SpecMaps are equivalent, zero otherwise.

*  Notes:
*     - A value of zero will be returned if this function is invoked
*     with the global status set, or if it should fail for any reason.
*/

/* Local Variables: */
   AstSpecMap *that;
   AstSpecMap *this;
   const char *argdesc[ MAX_ARGS ];
   const char *comment;
   int argdec;
   int argra;
   int i, j;
   int nargs;
   int nin;
   int nout;
   int result;
   int szargs;

/* Initialise. */
   result = 0;

/* Check the global error status. */
   if ( !astOK ) return result;

/* Obtain pointers to the two SpecMap structures. */
   this = (AstSpecMap *) this_object;
   that = (AstSpecMap *) that_object;

/* Check the second object is a SpecMap. We know the first is a
   SpecMap since we have arrived at this implementation of the virtual
   function. */
   if( astIsASpecMap( that ) ) {

/* Get the number of inputs and outputs and check they are the same for both. */
      nin = astGetNin( this );
      nout = astGetNout( this );
      if( astGetNin( that ) == nin && astGetNout( that ) == nout ) {

/* If the Invert flags for the two SpecMaps differ, it may still be possible
   for them to be equivalent. First compare the SpecMaps if their Invert
   flags are the same. In this case all the attributes of the two SpecMaps
   must be identical. */
         if( astGetInvert( this ) == astGetInvert( that ) ) {
            if( this->ncvt == that->ncvt ) {
               result = 1;
               for( i = 0; i < this->ncvt && result; i++ ) {
                  if( this->cvttype[ i ] != that->cvttype[ i ] ) {
                     result = 0;
                  } else {
                     CvtString( this->cvttype[ i ], &comment, &argra,
                                &argdec, &nargs, &szargs, argdesc, status );
                     for( j = 0; j < nargs; j++ ) {
                        if( !astEQUAL( this->cvtargs[ i ][ j ],
                                       that->cvtargs[ i ][ j ] ) ){
                           result = 0;
                           break;
                        }
                     }
                  }
               }
            }

/* If the Invert flags for the two SpecMaps differ, the attributes of the two
   SpecMaps must be inversely related to each other. */
         } else {

/* In the specific case of a SpecMap, Invert flags must be equal. */
            result = 0;

         }
      }
   }

/* If an error occurred, clear the result value. */
   if ( !astOK ) result = 0;

/* Return the result, */
   return result;
}

static int GetObjSize( AstObject *this_object, int *status ) {
/*
*  Name:
*     GetObjSize

*  Purpose:
*     Return the in-memory size of an Object.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     int GetObjSize( AstObject *this, int *status )

*  Class Membership:
*     SpecMap member function (over-rides the astGetObjSize protected
*     method inherited from the parent class).

*  Description:
*     This function returns the in-memory size of the supplied SpecMap,
*     in bytes.

*  Parameters:
*     this
*        Pointer to the SpecMap.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     The Object size, in bytes.

*  Notes:
*     - A value of zero will be returned if this function is invoked
*     with the global status set, or if it should fail for any reason.
*/

/* Local Variables: */
   AstSpecMap *this;         /* Pointer to SpecMap structure */
   int result;               /* Result value to return */
   int cvt;                  /* Loop counter for coordinate conversions */

/* Initialise. */
   result = 0;

/* Check the global error status. */
   if ( !astOK ) return result;

/* Obtain a pointers to the SpecMap structure. */
   this = (AstSpecMap *) this_object;

/* Invoke the GetObjSize method inherited from the parent class, and then
   add on any components of the class structure defined by thsi class
   which are stored in dynamically allocated memory. */
   result = (*parent_getobjsize)( this_object, status );

   for ( cvt = 0; cvt < this->ncvt; cvt++ ) {
      result += astTSizeOf( this->cvtargs[ cvt ] );
   }

   result += astTSizeOf( this->cvtargs );
   result += astTSizeOf( this->cvttype );

/* If an error occurred, clear the result value. */
   if ( !astOK ) result = 0;

/* Return the result, */
   return result;
}

static void AddSpecCvt( AstSpecMap *this, int cvttype, int narg,
                        const double *args, int *status ) {
/*
*  Name:
*     AddSpecCvt

*  Purpose:
*     Add a coordinate conversion step to an SpecMap.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     void AddSpecCvt( AstSpecMap *this, int cvttype, int narg,
*                      const double *args )

*  Class Membership:
*     SpecMap member function.

*  Description:
*     This function allows one of the supported spectral coordinate
*     conversions to be appended to a SpecMap. When a SpecMap is first
*     created (using astSpecMap), it simply performs a unit mapping. By
*     using AddSpecCvt repeatedly, a series of coordinate conversions may
*     then be specified which the SpecMap will subsequently perform in
*     sequence. This allows a complex coordinate conversion to be
*     assembled out of the basic building blocks. The SpecMap will also
*     perform the inverse coordinate conversion (applying the individual
*     conversion steps in reverse) if required.

*  Parameters:
*     this
*        Pointer to the SpecMap.
*     cvttype
*        A code to identify which spectral coordinate conversion is to be
*        appended.  See the "Coordinate Conversions" section for details
*        of those available.
*     narg
*        The number of argument values supplied in "args".
*     args
*        Pointer to an array of double containing the argument values
*        required to fully specify the required coordinate
*        conversion. The number of arguments depends on the conversion
*        (see the "Coordinate Conversions" section for details). This
*        value is ignored and may be NULL if no arguments are required.

*  Returned Value:
*     void.

*  Coordinate Conversions:
*     The following values may be supplied for the "cvttype" parameter
*     in order to specify the coordinate conversion to be performed.
*     The argument(s) required to fully specify each conversion are
*     indicated in parentheses after each value, and described at the end
*     of the list. Values for these should be given in the array pointed
*     at by "args".
*
*        AST__FRTOVL( RF )
*           Convert frequency to relativistic velocity.
*        AST__VLTOFR( RF )
*           Convert relativistic velocity to Frequency.
*        AST__ENTOFR
*           Convert energy to frequency.
*        AST__FRTOEN
*           Convert frequency to energy.
*        AST__WNTOFR
*           Convert wave number to frequency.
*        AST__FRTOWN
*           Convert frequency to wave number.
*        AST__WVTOFR
*           Convert wavelength (vacuum) to frequency.
*        AST__FRTOWV
*           Convert frequency to wavelength (vacuum).
*        AST__AWTOFR
*           Convert wavelength (air) to frequency.
*        AST__FRTOAW
*           Convert frequency to wavelength (air).
*        AST__VRTOVL
*           Convert radio to relativistic velocity.
*        AST__VLTOVR
*           Convert relativistic to radio velocity.
*        AST__VOTOVL
*           Convert optical to relativistic velocity.
*        AST__VLTOVO
*           Convert relativistic to optical velocity.
*        AST__ZOTOVL
*           Convert redshift to relativistic velocity.
*        AST__VLTOZO
*           Convert relativistic velocity to redshift.
*        AST__BTTOVL
*           Convert beta factor to relativistic velocity.
*        AST__VLTOBT
*           Convert relativistic velocity to beta factor.
*        AST_USF2HL( VOFF, RA, DEC )
*           Convert frequency from a user-defined reference frame to
*           heliocentric.
*        AST__HLF2US( VOFF, RA, DEC )
*           Convert frequency from heliocentric reference frame to
*           user-defined.
*        AST__TPF2HL( OBSLON, OBSLAT, OBSALT, EPOCH, RA, DEC )
*           Convert from Topocentric to heliocentric frequency
*        AST__HLF2TP( OBSLON, OBSLAT, OBSALT, EPOCH, RA, DEC )
*           Convert from Heliocentric to topocentric frequency.
*        AST__GEF2HL( EPOCH, RA, DEC )
*           Convert from Geocentric to heliocentric frequency.
*        AST__HLF2GE( EPOCH, RA, DEC )
*           Convert from Heliocentric to geocentric frequency.
*        AST__BYF2HL( EPOCH, RA, DEC )
*           Convert from Barycentric to heliocentric frequency.
*        AST__HLF2BY( EPOCH, RA, DEC )
*           Convert from Heliocentric to barycentric frequency.
*        AST__LKF2HL( RA, DEC )
*           Convert from LSRK to heliocentric frequency.
*        AST__HLF2LK( RA, DEC )
*           Convert from Heliocentric to LSRK frequency.
*        AST__LDF2HL( RA, DEC )
*           Convert from LSRD to heliocentric frequency.
*        AST__HLF2LD( RA, DEC )
*           Convert from Heliocentric to LSRD frequency.
*        AST__LGF2HL( RA, DEC )
*           Convert from Local group to heliocentric frequency.
*        AST__HLF2LG( RA, DEC )
*           Convert from Heliocentric to local group frequency.
*        AST__GLF2HL( RA, DEC )
*           Convert from Galactic to heliocentric frequency.
*        AST__HLF2GL( RA, DEC )
*           Convert from Heliocentric to galactic frequency.
*
*     The units for the values processed by the above conversions are as
*     follows:
*
*     - all velocities: metres per second.
*     - frequency: Hertz.
*     - all wavelengths: metres.
*     - energy: Joules.
*     - wave number: cycles per metre.
*
*     The arguments used in the above conversions are as follows:
*
*     - RF: Rest frequency (Hz).
*     - OBSALT: Geodetic altitude of observer (IAU 1975, metres).
*     - OBSLAT: Geodetic latitude of observer (IAU 1975, radians).
*     - OBSLON: Longitude of observer (radians, positive eastwards).
*     - EPOCH: Epoch of observation (UT1 expressed as a Modified Julian Date).
*     - RA: Right Ascension of source (radians, FK5 J2000).
*     - DEC: Declination of source (radians, FK5 J2000).
*     - VOFF: Velocity of the user-defined reference frame, towards the
*     position given by RA and DEC, measured in the heliocentric
*     reference frame.
*
*     If the SpecMap is 3-dimensional, source positions are provided by the
*     values supplied to inputs 2 and 3 of the SpecMap (which are simply
*     copied to outputs 2 and 3). Note, usable values are still required
*     for the RA and DEC arguments in order to define the "user-defined"
*     reference frame used by USF2HL and HLF2US. However, AST__BAD can be
*     supplied for RA and DEC if the user-defined reference frame is not
*     required.

*  Notes:
*     - The specified conversion is appended only if the SpecMap's
*     Invert attribute is zero. If it is non-zero, this function
*     effectively prefixes the inverse of the conversion specified
*     instead.
*/

/* Local Variables: */
   const char *argdesc[ MAX_ARGS ]; /* Pointers to argument descriptions */
   const char *comment;          /* Pointer to comment string */
   const char *cvt_string;       /* Pointer to conversion type string */
   int argdec;                   /* Index of DEC argument */
   int argra;                    /* Index of RA argument */
   int i;                        /* Argument index */
   int nargs;                    /* Number of user-supplied arguments */
   int ncvt;                     /* Number of coordinate conversions */
   int szargs;                   /* Size of arguments array */

/* Check the global error status. */
   if ( !astOK ) return;

/* Validate the coordinate conversion type and obtain the number of
   required user-supplied arguments, and the size of the array in which
   to put the user-supplied arguments (the array meay leave room after
   the user-supplied arguments for various useful pre-calculated values). */
   cvt_string = CvtString( cvttype, &comment, &argra, &argdec, &nargs,
                           &szargs, argdesc, status );

/* If the coordinate conversion type was not valid, then report an
   error. */
   if ( astOK && !cvt_string ) {
      astError( AST__SPCIN, "AddSpecCvt(%s): Invalid spectral coordinate "
                "conversion type (%d).", status, astGetClass( this ),
                (int) cvttype );
   }

/* If the number of supplied arguments is incorrect, then report an error. */
   if ( astOK && nargs != narg ) {
      astError( AST__TIMIN, "AddSpecCvt(%s): Invalid no. of arguments for spectral "
                "coordinate conversion type %d - %d supplied, %d required.",
                status, astGetClass( this ), (int) cvttype, narg, nargs );
   }

/* Note the number of coordinate conversions already stored in the SpecMap. */
   if ( astOK ) {
      ncvt = this->ncvt;

/* Extend the array of conversion types and the array of pointers to
   their argument lists to accommodate the new one. */
      this->cvttype = (int *) astGrow( this->cvttype, ncvt + 1,
                                       sizeof( int ) );
      this->cvtargs = (double **) astGrow( this->cvtargs, ncvt + 1,
                                           sizeof( double * ) );

/* If OK, allocate memory and store a copy of the argument list,
   putting a pointer to the copy into the SpecMap. */
      if ( astOK ) {
         this->cvtargs[ ncvt ] = astStore( NULL, args,
                                           sizeof( double ) * (size_t) szargs );
      }

/* Store the conversion type and increment the conversion count. Also put
   AST__BAD in any elements of the argument array which are beyond the
   end of the user-supplied arguments. These will be used to hold
   intermediate values calculated on the basis of the user-supplied
   arguments. */
      if ( astOK ) {
         this->cvttype[ ncvt ] = cvttype;
         this->ncvt++;
         for( i = nargs; i < szargs; i++ ) this->cvtargs[ ncvt ][ i ] = AST__BAD;
      }
   }
}

static double BaryVel( double ra, double dec, FrameDef *def, int *status ) {
/*
*  Name:
*     BaryVel

*  Purpose:
*     Find the velocity of the earth-sun barycentre away from the source.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     double BaryVel( double ra, double dec, FrameDef *def, int *status )

*  Class Membership:
*     SpecMap method.

*  Description:
*     This function finds the component of the velocity of the earth-sun
*     barycentre away from a specified source position, at a given epoch, in
*     the frame of rest of the centre of the Sun.

*  Parameters:
*     ra
*        The RA (rads, FK5 J2000) of the source.
*     dec
*        The Dec (rads, FK5 J2000) of the source.
*     def
*        Pointer to a FrameDef structure which holds the parameters which
*        define the frame, together with cached intermediate results.
*     status
*        Pointer to the inherited status variable.

*  Returns:
*     The component of the frame's velocity away from the position given by
*     "ra" and "dec", in m/s, measured within the Heliographic frame of
*     rest. Zero is returned if an error has already occurred.

*/

/* Local Variables: */
   double dpb[ 3 ];          /* Barycentric earth position vector */
   double dph[ 3 ];          /* Heliocentric earth position vector */
   double dvh[ 3 ];          /* Heliocentric earth velocity vector */
   double v[ 3 ];            /* Source direction vector */

/* Check the global error status. */
   if ( !astOK ) return 0.0;

/* Get the Cartesian vector towards the source, in the Cartesian FK5
   J2000 system. */
   palDcs2c( ra, dec, v );

/* If not already done so, get the Earth/Sun velocity and position vectors in
   the same system. Speed is returned in units of AU/s. Store in the supplied
   frame definition structure. */
   if( def->dvb[ 0 ] == AST__BAD ) {
      palEvp( def->epoch, 2000.0, def->dvb, dpb, dvh, dph );

/* Change the barycentric velocity of the earth into the heliocentric
   velocity of the barycentre. */
      def->dvb[ 0 ] = dvh[ 0 ] - def->dvb[ 0 ];
      def->dvb[ 1 ] = dvh[ 1 ] - def->dvb[ 1 ];
      def->dvb[ 2 ] = dvh[ 2 ] - def->dvb[ 2 ];
   }

/* Return the component away from the source, of the velocity of the
   barycentre relative to the sun (in m/s). */
   return -palDvdv( v, def->dvb )*149.597870E9;

}

static int CvtCode( const char *cvt_string, int *status ) {
/*
*  Name:
*     CvtCode

*  Purpose:
*     Convert a conversion type from a string representation to a code value.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     int CvtCode( const char *cvt_string, int *status )

*  Class Membership:
*     SpecMap member function.

*  Description:
*     This function accepts a string used to repersent one of the
*     SpecMap coordinate conversions and converts it into a code
*     value for internal use.

*  Parameters:
*     cvt_string
*        Pointer to a constant null-terminated string representing a
*        spectral coordinate conversion. This is case sensitive and should
*        contain no unnecessary white space.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     The equivalent conversion code. If the string was not
*     recognised, the code AST__SPEC_NULL is returned, without error.

*  Notes:
*     - A value of AST__SPEC_NULL will be returned if this function is
*     invoked with the global error status set, or if it should fail
*     for any reason.
*/

/* Local Variables: */
   int result;                   /* Result value to return */

/* Initialise. */
   result = AST__SPEC_NULL;

/* Check the global error status. */
   if ( !astOK ) return result;

/* Test the string against each recognised value in turn and assign
   the result. */
   if ( astChrMatch( cvt_string, "FRTOVL" ) ) {
      result = AST__FRTOVL;

   } else if ( astChrMatch( cvt_string, "VLTOFR" ) ) {
      result = AST__VLTOFR;

   } else if ( astChrMatch( cvt_string, "VLTOFR" ) ) {
      result = AST__VLTOFR;

   } else if ( astChrMatch( cvt_string, "ENTOFR" ) ) {
      result = AST__ENTOFR;

   } else if ( astChrMatch( cvt_string, "FRTOEN" ) ) {
      result = AST__FRTOEN;

   } else if ( astChrMatch( cvt_string, "WNTOFR" ) ) {
      result = AST__WNTOFR;

   } else if ( astChrMatch( cvt_string, "FRTOWN" ) ) {
      result = AST__FRTOWN;

   } else if ( astChrMatch( cvt_string, "WVTOFR" ) ) {
      result = AST__WVTOFR;

   } else if ( astChrMatch( cvt_string, "FRTOWV" ) ) {
      result = AST__FRTOWV;

   } else if ( astChrMatch( cvt_string, "AWTOFR" ) ) {
      result = AST__AWTOFR;

   } else if ( astChrMatch( cvt_string, "FRTOAW" ) ) {
      result = AST__FRTOAW;

   } else if ( astChrMatch( cvt_string, "VRTOVL" ) ) {
      result = AST__VRTOVL;

   } else if ( astChrMatch( cvt_string, "VLTOVR" ) ) {
      result = AST__VLTOVR;

   } else if ( astChrMatch( cvt_string, "VOTOVL" ) ) {
      result = AST__VOTOVL;

   } else if ( astChrMatch( cvt_string, "VLTOVO" ) ) {
      result = AST__VLTOVO;

   } else if ( astChrMatch( cvt_string, "ZOTOVL" ) ) {
      result = AST__ZOTOVL;

   } else if ( astChrMatch( cvt_string, "VLTOZO" ) ) {
      result = AST__VLTOZO;

   } else if ( astChrMatch( cvt_string, "BTTOVL" ) ) {
      result = AST__BTTOVL;

   } else if ( astChrMatch( cvt_string, "VLTOBT" ) ) {
      result = AST__VLTOBT;

   } else if ( astChrMatch( cvt_string, "USF2HL" ) ) {
      result = AST__USF2HL;

   } else if ( astChrMatch( cvt_string, "HLF2US" ) ) {
      result = AST__HLF2US;

   } else if ( astChrMatch( cvt_string, "TPF2HL" ) ) {
      result = AST__TPF2HL;

   } else if ( astChrMatch( cvt_string, "HLF2TP" ) ) {
      result = AST__HLF2TP;

   } else if ( astChrMatch( cvt_string, "GEF2HL" ) ) {
      result = AST__GEF2HL;

   } else if ( astChrMatch( cvt_string, "HLF2GE" ) ) {
      result = AST__HLF2GE;

   } else if ( astChrMatch( cvt_string, "BYF2HL" ) ) {
      result = AST__BYF2HL;

   } else if ( astChrMatch( cvt_string, "HLF2BY" ) ) {
      result = AST__HLF2BY;

   } else if ( astChrMatch( cvt_string, "LKF2HL" ) ) {
      result = AST__LKF2HL;

   } else if ( astChrMatch( cvt_string, "HLF2LK" ) ) {
      result = AST__HLF2LK;

   } else if ( astChrMatch( cvt_string, "LDF2HL" ) ) {
      result = AST__LDF2HL;

   } else if ( astChrMatch( cvt_string, "HLF2LD" ) ) {
      result = AST__HLF2LD;

   } else if ( astChrMatch( cvt_string, "LGF2HL" ) ) {
      result = AST__LGF2HL;

   } else if ( astChrMatch( cvt_string, "HLF2LG" ) ) {
      result = AST__HLF2LG;

   } else if ( astChrMatch( cvt_string, "GLF2HL" ) ) {
      result = AST__GLF2HL;

   } else if ( astChrMatch( cvt_string, "HLF2GL" ) ) {
      result = AST__HLF2GL;

   }

/* Return the result. */
   return result;
}

static const char *CvtString( int cvt_code, const char **comment,
                              int *argra, int *argdec, int *nargs, int *szargs,
                              const char *arg[ MAX_ARGS ], int *status ) {
/*
*  Name:
*     CvtString

*  Purpose:
*     Convert a conversion type from a code value to a string representation.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     const char *CvtString( int cvt_code, const char **comment,
*                            int *argra, int *argdec, int *nargs,
*                            int *szargs, const char *arg[ MAX_ARGS ], int *status )

*  Class Membership:
*     SpecMap member function.

*  Description:
*     This function accepts a code value used to represent one of the
*     SpecMap coordinate conversions and converts it into an
*     equivalent string representation. It also returns a descriptive
*     comment and information about the arguments required in order to
*     perform the conversion.

*  Parameters:
*     cvt_code
*        The conversion code.
*     comment
*        Address of a location to return a pointer to a constant
*        null-terminated string containing a description of the
*        conversion.
*     argra
*        Address of an int in which to return the index of the argument
*        corresponding to the source RA. Returned equal to -1 if the
*        conversion does not have a source RA argument.
*     argdec
*        Address of an int in which to return the index of the argument
*        corresponding to the source DEC. Returned equal to -1 if the
*        conversion does not have a source DEC argument.
*     nargs
*        Address of an int in which to return the number of arguments
*        required from the user in order to perform the conversion (may
*        be zero).
*     szargs
*        Address of an int in which to return the number of arguments
*        associated with the conversion. This may be bigger than "nargs"
*        if the conversion can pre-calculate useful values on the basis
*        of the user-supplied values. Such precalculated values are
*        stored after the last user-supplied argument.
*     arg
*        An array in which to return a pointer to a constant
*        null-terminated string for each argument (above) containing a
*        description of what each argument represents. This includes both
*        user-supplied arguments and pre-calculated values.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     Pointer to a constant null-terminated string representation of
*     the conversion code value supplied. If the code supplied is not
*     valid, a NULL pointer will be returned, without error.

*  Notes:
*     - A NULL pointer value will be returned if this function is
*     invoked with the global error status set, or if it should fail
*     for any reason.
*/

/* Local Variables: */
   const char *result;          /* Result pointer to return */

/* Initialise the returned values. */
   *comment = NULL;
   *nargs = 0;
   *argra = -1;
   *argdec = -1;
   result = NULL;

/* Check the global error status. */
   if ( !astOK ) return result;

/* Test for each valid code value in turn and assign the appropriate
   return values. */
   switch ( cvt_code ) {

   case AST__FRTOVL:
      *comment = "Convert frequency to rel. velocity";
      result = "FRTOVL";
      *nargs = 1;
      *szargs = 1;
      arg[ 0 ] = "Rest frequency (Hz)";
      break;

   case AST__VLTOFR:
      *comment = "Convert rel. velocity to frequency";
      result = "VLTOFR";
      *nargs = 1;
      *szargs = 1;
      arg[ 0 ] = "Rest frequency (Hz)";
      break;

   case AST__ENTOFR:
      *comment = "Convert energy to frequency";
      result = "ENTOFR";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__FRTOEN:
      *comment = "Convert frequency to energy";
      result = "FRTOEN";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__WNTOFR:
      *comment = "Convert wave number to frequency";
      result = "WNTOFR";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__FRTOWN:
      *comment = "Convert frequency to wave number";
      result = "FRTOWN";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__WVTOFR:
      *comment = "Convert wavelength (vacuum) to frequency";
      result = "WVTOFR";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__FRTOWV:
      *comment = "Convert frequency to wavelength (vacuum)";
      result = "FRTOWV";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__AWTOFR:
      *comment = "Convert wavelength (air) to frequency";
      result = "AWTOFR";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__FRTOAW:
      *comment = "Convert frequency to wavelength (air)";
      result = "FRTOAW";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__VRTOVL:
      *comment = "Convert radio to rel. velocity";
      result = "VRTOVL";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__VLTOVR:
      *comment = "Convert relativistic to radio velocity";
      result = "VLTOVR";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__VOTOVL:
      *comment = "Convert optical to rel. velocity";
      result = "VOTOVL";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__VLTOVO:
      *comment = "Convert relativistic to optical velocity";
      result = "VLTOVO";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__ZOTOVL:
      *comment = "Convert redshift to rel. velocity";
      result = "ZOTOVL";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__VLTOZO:
      *comment = "Convert rel. velocity to redshift";
      result = "VLTOZO";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__BTTOVL:
      *comment = "Convert beta factor to rel. velocity";
      result = "BTTOVL";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__VLTOBT:
      *comment = "Convert rel. velocity to beta factor";
      result = "VLTOBT";
      *nargs = 0;
      *szargs = 0;
      break;

   case AST__USF2HL:
      *comment = "Convert from user-defined to heliocentric frequency";
      result = "USF2HL";
      *argra = 1;
      *argdec = 2;
      *nargs = 3;
      *szargs = 4;
      arg[ 0 ] = "Velocity offset (m/s)";
      arg[ 1 ] = "RA of source (FK5 J2000, radians)";
      arg[ 2 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 3 ] = "Frequency correction factor";
      break;

   case AST__HLF2US:
      *comment = "Convert from heliocentric to user-defined frequency";
      result = "HLF2US";
      *argra = 1;
      *argdec = 2;
      *nargs = 3;
      *szargs = 4;
      arg[ 0 ] = "Velocity offset (m/s)";
      arg[ 1 ] = "RA of source (FK5 J2000, radians)";
      arg[ 2 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 3 ] = "Frequency correction factor";
      break;

   case AST__TPF2HL:
      *comment = "Convert from Topocentric to heliocentric frequency";
      result = "TPF2HL";
      *argra = 4;
      *argdec = 5;
      *nargs = 6;
      *szargs = 7;
      arg[ 0 ] = "Longitude (positive eastwards, radians)";
      arg[ 1 ] = "Latitude (geodetic, radians)";
      arg[ 2 ] = "Altitude (geodetic, metres)";
      arg[ 3 ] = "UT1 epoch of observaton (Modified Julian Date)";
      arg[ 4 ] = "RA of source (FK5 J2000, radians)";
      arg[ 5 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 6 ] = "Frequency correction factor";
      break;

   case AST__HLF2TP:
      *comment = "Convert from Heliocentric to topocentric frequency";
      result = "HLF2TP";
      *argra = 4;
      *argdec = 5;
      *nargs = 6;
      *szargs = 7;
      arg[ 0 ] = "Longitude (positive eastwards, radians)";
      arg[ 1 ] = "Latitude (geodetic, radians)";
      arg[ 2 ] = "Altitude (geodetic, metres)";
      arg[ 3 ] = "UT1 epoch of observaton (Modified Julian Date)";
      arg[ 4 ] = "RA of source (FK5 J2000, radians)";
      arg[ 5 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 6 ] = "Frequency correction factor";
      break;

   case AST__GEF2HL:
      *comment = "Convert from Geocentric to heliocentric frequency";
      result = "GEF2HL";
      *argra = 1;
      *argdec = 2;
      *nargs = 3;
      *szargs = 4;
      arg[ 0 ] = "UT1 epoch of observaton (Modified Julian Date)";
      arg[ 1 ] = "RA of source (FK5 J2000, radians)";
      arg[ 2 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 3 ] = "Frequency correction factor";
      break;

   case AST__HLF2GE:
      *comment = "Convert from Heliocentric to geocentric frequency";
      result = "HLF2GE";
      *argra = 1;
      *argdec = 2;
      *nargs = 3;
      *szargs = 4;
      arg[ 0 ] = "UT1 epoch of observaton (Modified Julian Date)";
      arg[ 1 ] = "RA of source (FK5 J2000, radians)";
      arg[ 2 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 3 ] = "Frequency correction factor";
      break;

   case AST__BYF2HL:
      *comment = "Convert from Barycentric to heliocentric frequency";
      result = "BYF2HL";
      *argra = 1;
      *argdec = 2;
      *nargs = 3;
      *szargs = 4;
      arg[ 0 ] = "UT1 epoch of observaton (Modified Julian Date)";
      arg[ 1 ] = "RA of source (FK5 J2000, radians)";
      arg[ 2 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 3 ] = "Frequency correction factor";
      break;

   case AST__HLF2BY:
      *comment = "Convert from Heliocentric to barycentric frequency";
      result = "HLF2BY";
      *argra = 1;
      *argdec = 2;
      *nargs = 3;
      *szargs = 4;
      arg[ 0 ] = "UT1 epoch of observaton (Modified Julian Date)";
      arg[ 1 ] = "RA of source (FK5 J2000, radians)";
      arg[ 2 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 3 ] = "Frequency correction factor";
      break;

   case AST__LKF2HL:
      *comment = "Convert from LSRK to heliocentric frequency";
      result = "LKF2HL";
      *argra = 0;
      *argdec = 1;
      *nargs = 2;
      *szargs = 3;
      arg[ 0 ] = "RA of source (FK5 J2000, radians)";
      arg[ 1 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 2 ] = "Frequency correction factor";
      break;

   case AST__HLF2LK:
      *comment = "Convert from Heliocentric to LSRK frequency";
      result = "HLF2LK";
      *argra = 0;
      *argdec = 1;
      *nargs = 2;
      *szargs = 3;
      arg[ 0 ] = "RA of source (FK5 J2000, radians)";
      arg[ 1 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 2 ] = "Frequency correction factor";
      break;

   case AST__LDF2HL:
      *comment = "Convert from LSRD to heliocentric frequency";
      result = "LDF2HL";
      *argra = 0;
      *argdec = 1;
      *nargs = 2;
      *szargs = 3;
      arg[ 0 ] = "RA of source (FK5 J2000, radians)";
      arg[ 1 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 2 ] = "Frequency correction factor";
      break;

   case AST__HLF2LD:
      *comment = "Convert from Heliocentric to LSRD frequency";
      result = "HLF2LD";
      *argra = 0;
      *argdec = 1;
      *nargs = 2;
      *szargs = 3;
      arg[ 0 ] = "RA of source (FK5 J2000, radians)";
      arg[ 1 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 2 ] = "Frequency correction factor";
      break;

   case AST__LGF2HL:
      *comment = "Convert from Local group to heliocentric frequency";
      result = "LGF2HL";
      *argra = 0;
      *argdec = 1;
      *nargs = 2;
      *szargs = 3;
      arg[ 0 ] = "RA of source (FK5 J2000, radians)";
      arg[ 1 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 2 ] = "Frequency correction factor";
      break;

   case AST__HLF2LG:
      *comment = "Convert from Heliocentric to local group frequency";
      result = "HLF2LG";
      *argra = 0;
      *argdec = 1;
      *nargs = 2;
      *szargs = 3;
      arg[ 0 ] = "RA of source (FK5 J2000, radians)";
      arg[ 1 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 2 ] = "Frequency correction factor";
      break;

   case AST__GLF2HL:
      *comment = "Convert from Galactic to heliocentric frequency";
      result = "GLF2HL";
      *argra = 0;
      *argdec = 1;
      *nargs = 2;
      *szargs = 3;
      arg[ 0 ] = "RA of source (FK5 J2000, radians)";
      arg[ 1 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 2 ] = "Frequency correction factor";
      break;

   case AST__HLF2GL:
      *comment = "Convert from Heliocentric to galactic frequency";
      *argra = 0;
      *argdec = 1;
      result = "HLF2GL";
      *nargs = 2;
      *szargs = 3;
      arg[ 0 ] = "RA of source (FK5 J2000, radians)";
      arg[ 1 ] = "DEC of source (FK5 J2000, radians)";
      arg[ 2 ] = "Frequency correction factor";
      break;

   }

/* Return the result. */
   return result;
}

static int FrameChange( int cvt_code, int np, double *ra, double *dec, double *freq,
                        double *args, int forward, int *status ){
/*
*  Name:
*     FrameChange

*  Purpose:
*     Apply a doppler shift caused by a change of reference frame.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     int FrameChange( int cvt_code, int np, double *ra, double *dec,
*                      double *freq, double *args, int forward, int *status )

*  Class Membership:
*     SpecMap method.

*  Description:
*     This function modifies the supplied frequency values in order to
*     apply a doppler shift caused by a change of the observers rest-frame.

*  Parameters:
*     cvt_code
*        A code indicating the conversion to be applied. If the code does
*        not correspond to a change of rest-frame, then the supplied
*        frequencies are left unchanged and zero is returned as the
*        function value.
*     np
*        The number of frequency values to transform.
*     ra
*        Pointer to an array of "np" RA (J2000 FK5) values at which the
*        "np" frequencies are observed. These are unchanged on exit. If a
*        NULL pointer is supplied, then all frequencies are assumed to be
*        observed at the single RA value given by "refra"
*     dec
*        Pointer to an array of "np" Dec (J2000 FK5) values at which the
*        "np" frequencies are observed. These are unchanged on exit. If a
*        NULL pointer is supplied, then all frequencies are assumed to be
*        observed at the single Dec value given by "refdec"
*     freq
*        Pointer to an array of "np" frequency values, measured in the
*        input rest-frame. These are modified on return to hold the
*        corresponding values measured in the output rest-frame.
*     args
*        Pointer to an array holding the conversion arguments. The number
*        of arguments expected depends on the particular conversion being
*        used.
*     forward
*        Should the conversion be applied in the forward or inverse
*        direction? Non-zero for forward, zero for inverse.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     Non-zero if the supplied conversion code corresponds to a change of
*     reference frame. Zoer otherwise  (in which case the upplied values
*     will not have been changed).

*  Notes:
*     - The "args" array contains RA and DEC values which give the "source"
*     position (FK5 J2000). If a NULL value is supplied for the "ra"
*     parameter, then these args define the position of all the frequency
*     values. In addition they also define the direction of motion of
*     the "user-defined" rest-frame (see "veluser"). Thus they should still
*     be supplied even if "ra" is NULL.

*/

/* Local Variables: */
   FrameDef def;      /* Structure holding frame parameters */
   double (* cvtFunc)( double, double, FrameDef *, int * ); /* Pointer to conversion function */
   double *fcorr;     /* Pointer to frequency correction factor */
   double *pdec;      /* Pointer to next Dec value */
   double *pf;        /* Pointer to next frequency value */
   double *pra;       /* Pointer to next RA value */
   double factor;     /* Frequency correction factor */
   double s;          /* Velocity correction (m/s) */
   int i;             /* Loop index */
   int result;        /* Returned value */
   int sign;          /* Sign for velocity correction */

/* Check inherited status. */
   if( !astOK ) return 0;

/* Initialise */
   cvtFunc = NULL;
   fcorr = NULL;
   sign = 0;

/* Set the return value to indicate that the supplied conversion code
   represents a change of rest-frame. */
   result = 1;

/* Initialise a structure which stores parameters which define the
   transformation. */
   def.obsalt = AST__BAD;
   def.obslat = AST__BAD;
   def.obslon = AST__BAD;
   def.epoch = AST__BAD;
   def.refdec = AST__BAD;
   def.refra = AST__BAD;
   def.veluser = AST__BAD;
   def.last = AST__BAD;
   def.amprms[ 0 ] = AST__BAD;
   def.vuser[ 0 ] = AST__BAD;
   def.dvh[ 0 ] = AST__BAD;
   def.dvb[ 0 ] = AST__BAD;

/* Test for each rest-frame code value in turn and assign the appropriate
   values. */
   switch ( cvt_code ) {

   case AST__USF2HL:
      cvtFunc = UserVel;
      def.veluser = args[ 0 ];
      def.refra = args[ 1 ];
      def.refdec = args[ 2 ];
      fcorr = args + 3;
      sign = -1;
      break;

   case AST__HLF2US:
      cvtFunc = UserVel;
      def.veluser = args[ 0 ];
      def.refra = args[ 1 ];
      def.refdec = args[ 2 ];
      fcorr = args + 3;
      sign = +1;
      break;

   case AST__TPF2HL:
      cvtFunc = TopoVel;
      def.obslon = args[ 0 ];
      def.obslat = args[ 1 ];
      def.obsalt = args[ 2 ];
      def.epoch = args[ 3 ];
      def.refra = args[ 4 ];
      def.refdec = args[ 5 ];
      fcorr = args + 6;
      sign = -1;
      break;

   case AST__HLF2TP:
      cvtFunc = TopoVel;
      def.obslon = args[ 0 ];
      def.obslat = args[ 1 ];
      def.obsalt = args[ 2 ];
      def.epoch = args[ 3 ];
      def.refra = args[ 4 ];
      def.refdec = args[ 5 ];
      fcorr = args + 6;
      sign = +1;
      break;

   case AST__GEF2HL:
      cvtFunc = GeoVel;
      def.epoch = args[ 0 ];
      def.refra = args[ 1 ];
      def.refdec = args[ 2 ];
      fcorr = args + 3;
      sign = -1;
      break;

   case AST__HLF2GE:
      cvtFunc = GeoVel;
      def.epoch = args[ 0 ];
      def.refra = args[ 1 ];
      def.refdec = args[ 2 ];
      fcorr = args + 3;
      sign = +1;
      break;

   case AST__BYF2HL:
      cvtFunc = BaryVel;
      def.epoch = args[ 0 ];
      def.refra = args[ 1 ];
      def.refdec = args[ 2 ];
      fcorr = args + 3;
      sign = -1;
      break;

   case AST__HLF2BY:
      cvtFunc = BaryVel;
      def.epoch = args[ 0 ];
      def.refra = args[ 1 ];
      def.refdec = args[ 2 ];
      fcorr = args + 3;
      sign = +1;
      break;

   case AST__LKF2HL:
      cvtFunc = LsrkVel;
      def.refra = args[ 0 ];
      def.refdec = args[ 1 ];
      fcorr = args + 2;
      sign = -1;
      break;

   case AST__HLF2LK:
      cvtFunc = LsrkVel;
      def.refra = args[ 0 ];
      def.refdec = args[ 1 ];
      fcorr = args + 2;
      sign = +1;
      break;

   case AST__LDF2HL:
      cvtFunc = LsrdVel;
      def.refra = args[ 0 ];
      def.refdec = args[ 1 ];
      fcorr = args + 2;
      sign = -1;
      break;

   case AST__HLF2LD:
      cvtFunc = LsrdVel;
      def.refra = args[ 0 ];
      def.refdec = args[ 1 ];
      fcorr = args + 2;
      sign = +1;
      break;

   case AST__LGF2HL:
      cvtFunc = LgVel;
      def.refra = args[ 0 ];
      def.refdec = args[ 1 ];
      fcorr = args + 2;
      sign = -1;
      break;

   case AST__HLF2LG:
      cvtFunc = LgVel;
      def.refra = args[ 0 ];
      def.refdec = args[ 1 ];
      fcorr = args + 2;
      sign = +1;
      break;

   case AST__GLF2HL:
      cvtFunc = GalVel;
      def.refra = args[ 0 ];
      def.refdec = args[ 1 ];
      fcorr = args + 2;
      sign = -1;
      break;

   case AST__HLF2GL:
      cvtFunc = GalVel;
      def.refra = args[ 0 ];
      def.refdec = args[ 1 ];
      fcorr = args + 2;
      sign = +1;
      break;

/* If the supplied code does not represent a change of rest-frame, clear
   the returned flag. */
   default:
      result = 0;
   }

/* Check we have a rest-frame code. */
   if( result ) {

/* First deal with cases where we have a single source position (given by
   refra and refdec). */
      if( !ra ) {

/* If the frequency correction factor has not been found, find it now. */
         if( *fcorr == AST__BAD ) {

/* Get the velocity correction. This is the component of the velocity of the
   output system, away from the source, as measured in the input system. */
            s = sign*cvtFunc( def.refra, def.refdec, &def, status );

/* Find the factor by which to correct supplied frequencies. If the
   velocity correction is positive, the output frequency wil be lower than
   the input frequency. */
            if( s < AST__C && s > -AST__C ) {
               *fcorr = sqrt( ( AST__C - s )/( AST__C + s ) );
            }
         }

/* Correct each supplied frequency. */
         if( *fcorr != AST__BAD && *fcorr != 0.0 ) {
            factor = forward ? *fcorr : 1.0 / ( *fcorr );
            pf = freq;
            for( i = 0; i < np; i++, pf++ ) {
               if( *pf != AST__BAD ) *pf *= factor;
            }

/* Set returned values bad if the velocity correction is un-physical. */
         } else {
            pf = freq;
            for( i = 0; i < np; i++ ) *(pf++) = AST__BAD;
         }

/* Now deal with cases where each frequency value has its own source
   position. */
      } else {

/* Invert the sign if we are doing a inverse transformation. */
         if( !forward ) sign = -sign;

/* Loop round each value. */
         pf = freq;
         pra = ra;
         pdec = dec;
         for( i = 0; i < np; i++ ) {

/* If the ra or dec is bad, store a bad frequency. */
            if( *pra == AST__BAD || *pdec == AST__BAD || *pf == AST__BAD ) {
               *pf = AST__BAD;

/* Otherwise, produce a corrected frequency. */
            } else {

/* Get the velocity correction. */
               s = sign*cvtFunc( *pra, *pdec, &def, status );

/* Correct this frequency, if possible. Otherwise set bad. */
               if( s < AST__C && s > -AST__C ) {
                  *pf *= sqrt( ( AST__C - s )/( AST__C + s ) );
               } else {
                  *pf = AST__BAD;
               }
            }

/* Move on to the next position. */
            pf++;
            pra++;
            pdec++;
         }
      }
   }

/* Return the result. */
   return result;
}

static double GalVel( double ra, double dec, FrameDef *def, int *status ) {
/*
*  Name:
*     GalVel

*  Purpose:
*     Find the velocity of the galactic centre away from the source.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     double GalVel( double ra, double dec, FrameDef *def, int *status )

*  Class Membership:
*     SpecMap method.

*  Description:
*     This function finds the component of the velocity of the galactic
*     centre away from a specified source position, in the frame of rest
*     of the Sun.

*  Parameters:
*     ra
*        The RA (rads, FK5 J2000) of the source.
*     dec
*        The Dec (rads, FK5 J2000) of the source.
*     def
*        Pointer to a FrameDef structure which holds the parameters which
*        define the frame, together with cached intermediate results.
*     status
*        Pointer to the inherited status variable.

*  Returns:
*     The component of the frame's velocity away from the position given by
*     "ra" and "dec", in m/s, measured within the Heliographic frame of
*     rest. Zero is returned if an error has already occurred.

*/

/* Local Variables: */
   double s1, s2;

/* Check the global error status. */
   if ( !astOK ) return 0.0;

/* Get the component away from the source, of the velocity of the sun
   relative to the dynamic LSR (in km/s). */
   s1 = (double) palRvlsrd( (float) ra, (float) dec );

/* Get the component away from the source, of the velocity of the
   dynamic LSR relative to the galactic centre (in km/s). */
   s2 = (double) palRvgalc( (float) ra, (float) dec );

/* Return the total velocity of the galactic centre away from the source,
   relative to the sun, in m/s. */
   return -1000.0*( s1 + s2 );
}

static double GeoVel( double ra, double dec, FrameDef *def, int *status ) {
/*
*  Name:
*     GeoVel

*  Purpose:
*     Find the velocity of the earth away from the source.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     double GeoVel( double ra, double dec, FrameDef *def, int *status )

*  Class Membership:
*     SpecMap method.

*  Description:
*     This function finds the component of the velocity of the earth away
*     from a specified source position, at a given epoch, in the frame of
*     rest of the Sun.

*  Parameters:
*     ra
*        The RA (rads, FK5 J2000) of the source.
*     dec
*        The Dec (rads, FK5 J2000) of the source.
*     def
*        Pointer to a FrameDef structure which holds the parameters which
*        define the frame, together with cached intermediate results.
*     status
*        Pointer to the inherited status variable.

*  Returns:
*     The component of the frame's velocity away from the position given by
*     "ra" and "dec", in m/s, measured within the Heliographic frame of
*     rest. Zero is returned if an error has already occurred.

*/

/* Local Variables: */
   double dpb[ 3 ];          /* Barycentric earth position vector */
   double dph[ 3 ];          /* Heliocentric earth position vector */
   double dvb[ 3 ];          /* Barycentric earth velocity vector */
   double v[ 3 ];            /* Source direction vector */

/* Check the global error status. */
   if ( !astOK ) return 0.0;

/* Get the Cartesian vector towards the source, in the Cartesian FK5
   J2000 system. */
   palDcs2c( ra, dec, v );

/* If not already done so, get the Earth/Sun velocity and position vectors in
   the same system. Speed is returned in units of AU/s. Store in the supplied
   frame definition structure. */
   if( def->dvh[ 0 ] == AST__BAD ) palEvp( def->epoch, 2000.0, dvb, dpb,
                                           def->dvh, dph );

/* Return the component away from the source, of the velocity of the earths
   centre relative to the sun (in m/s). */
   return -palDvdv( v, def->dvh )*149.597870E9;
}

void astInitSpecMapVtab_(  AstSpecMapVtab *vtab, const char *name, int *status ) {
/*
*+
*  Name:
*     astInitSpecMapVtab

*  Purpose:
*     Initialise a virtual function table for a SpecMap.

*  Type:
*     Protected function.

*  Synopsis:
*     #include "specmap.h"
*     void astInitSpecMapVtab( AstSpecMapVtab *vtab, const char *name )

*  Class Membership:
*     SpecMap vtab initialiser.

*  Description:
*     This function initialises the component of a virtual function
*     table which is used by the SpecMap class.

*  Parameters:
*     vtab
*        Pointer to the virtual function table. The components used by
*        all ancestral classes will be initialised if they have not already
*        been initialised.
*     name
*        Pointer to a constant null-terminated character string which contains
*        the name of the class to which the virtual function table belongs (it
*        is this pointer value that will subsequently be returned by the Object
*        astClass function).
*-
*/

/* Local Variables: */
   astDECLARE_GLOBALS            /* Pointer to thread-specific global data */
   AstObjectVtab *object;        /* Pointer to Object component of Vtab */
   AstMappingVtab *mapping;      /* Pointer to Mapping component of Vtab */

/* Check the local error status. */
   if ( !astOK ) return;

/* Get a pointer to the thread specific global data structure. */
   astGET_GLOBALS(NULL);

/* Initialize the component of the virtual function table used by the
   parent class. */
   astInitMappingVtab( (AstMappingVtab *) vtab, name );

/* Store a unique "magic" value in the virtual function table. This
   will be used (by astIsASpecMap) to determine if an object belongs to
   this class.  We can conveniently use the address of the (static)
   class_check variable to generate this unique value. */
   vtab->id.check = &class_check;
   vtab->id.parent = &(((AstMappingVtab *) vtab)->id);

/* Initialise member function pointers. */
/* ------------------------------------ */
/* Store pointers to the member functions (implemented here) that
   provide virtual methods for this class. */
   vtab->SpecAdd = SpecAdd;

/* Save the inherited pointers to methods that will be extended, and
   replace them with pointers to the new member functions. */
   object = (AstObjectVtab *) vtab;
   mapping = (AstMappingVtab *) vtab;
   parent_getobjsize = object->GetObjSize;
   object->GetObjSize = GetObjSize;

   parent_transform = mapping->Transform;
   mapping->Transform = Transform;

   parent_rate = mapping->Rate;
   mapping->Rate = Rate;

/* Store replacement pointers for methods which will be over-ridden by
   new member functions implemented here. */
   object->Equal = Equal;
   mapping->MapMerge = MapMerge;

/* Declare the copy constructor, destructor and class dump
   function. */
   astSetCopy( vtab, Copy );
   astSetDelete( vtab, Delete );
   astSetDump( vtab, Dump, "SpecMap",
               "Conversion between spectral coordinate systems" );

/* If we have just initialised the vtab for the current class, indicate
   that the vtab is now initialised, and store a pointer to the class
   identifier in the base "object" level of the vtab. */
   if( vtab == &class_vtab ) {
      class_init = 1;
      astSetVtabClassIdentifier( vtab, &(vtab->id) );
   }
}

static double LgVel( double ra, double dec, FrameDef *def, int *status ) {
/*
*  Name:
*     LgVel

*  Purpose:
*     Find the velocity of the Local Group away from the source.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     double LgVel( double ra, double dec, FrameDef *def, int *status )

*  Class Membership:
*     SpecMap method.

*  Description:
*     This function finds the component of the Local Group velocity away
*     from a specified source position, in the frame of rest of the Sun.

*  Parameters:
*     ra
*        The RA (rads, FK5 J2000) of the source.
*     dec
*        The Dec (rads, FK5 J2000) of the source.
*     def
*        Pointer to a FrameDef structure which holds the parameters which
*        define the frame, together with cached intermediate results.
*     status
*        Pointer to the inherited status variable.

*  Returns:
*     The component of the frame's velocity away from the position given by
*     "ra" and "dec", in m/s, measured within the Heliographic frame of
*     rest. Zero is returned if an error has already occurred.

*/

/* Return the component away from the source, of the velocity of the
   local group relative to the sun (in m/s). */
   return -1000.0*palRvlg( (float) ra, (float) dec );
}

static double LsrdVel( double ra, double dec, FrameDef *def, int *status ) {
/*
*  Name:
*     LsrdVel

*  Purpose:
*     Find the velocity of the Dynamical LSR away from the source.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     double LsrdVel( double ra, double dec, FrameDef *def, int *status )

*  Class Membership:
*     SpecMap method.

*  Description:
*     This function finds the component of the velocity of the Dynamical
*     LSR away from a specified source position, in the frame of rest of
*     the Sun.

*  Parameters:
*     ra
*        The RA (rads, FK5 J2000) of the source.
*     dec
*        The Dec (rads, FK5 J2000) of the source.
*     def
*        Pointer to a FrameDef structure which holds the parameters which
*        define the frame, together with cached intermediate results.
*     status
*        Pointer to the inherited status variable.

*  Returns:
*     The component of the frame's velocity away from the position given by
*     "ra" and "dec", in m/s, measured within the Heliographic frame of
*     rest. Zero is returned if an error has already occurred.

*/
/* Check the global error status. */
   if ( !astOK ) return 0.0;

/* Get the component away from the source, of the velocity of the sun
   relative to the dynamical LSR (in m/s). This can also be thought of as the
   velocity of the LSR towards the source relative to the sun. Return the
   negated value (i.e. velocity of lsrd *away from* the source. */
   return -1000.0*palRvlsrd( (float) ra, (float) dec );
}

static double LsrkVel( double ra, double dec, FrameDef *def, int *status ) {
/*
*  Name:
*     LsrkVel

*  Purpose:
*     Find the velocity of the Kinematic LSR away from the source.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     double LsrkVel( double ra, double dec, FrameDef *def, int *status )

*  Class Membership:
*     SpecMap method.

*  Description:
*     This function finds the component of the velocity of the Kinematic
*     LSR away from a specified source position, in the frame of rest of
*     the Sun.

*  Parameters:
*     ra
*        The RA (rads, FK5 J2000) of the source.
*     dec
*        The Dec (rads, FK5 J2000) of the source.
*     def
*        Pointer to a FrameDef structure which holds the parameters which
*        define the frame, together with cached intermediate results.
*     status
*        Pointer to the inherited status variable.

*  Returns:
*     The component of the frame's velocity away from the position given by
*     "ra" and "dec", in m/s, measured within the Heliographic frame of
*     rest. Zero is returned if an error has already occurred.

*/
/* Check the global error status. */
   if ( !astOK ) return 0.0;

/* Get the component away from the source, of the velocity of the sun
   relative to the kinematic LSR (in m/s). This can also be thought of as the
   velocity of the LSR towards the source relative to the sun. Return the
   negated value (i.e. velocity of lsrk *away from* the source. */
   return -1000.0*palRvlsrk( (float) ra, (float) dec );
}

static int MapMerge( AstMapping *this, int where, int series, int *nmap,
                     AstMapping ***map_list, int **invert_list, int *status ) {
/*
*  Name:
*     MapMerge

*  Purpose:
*     Simplify a sequence of Mappings containing a SpecMap.

*  Type:
*     Private function.

*  Synopsis:
*     #include "mapping.h
*     int MapMerge( AstMapping *this, int where, int series, int *nmap,
*                   AstMapping ***map_list, int **invert_list, int *status )

*  Class Membership:
*     SpecMap method (over-rides the protected astMapMerge method
*     inherited from the Mapping class).

*  Description:
*     This function attempts to simplify a sequence of Mappings by
*     merging a nominated SpecMap in the sequence with its neighbours,
*     so as to shorten the sequence if possible.
*
*     In many cases, simplification will not be possible and the
*     function will return -1 to indicate this, without further
*     action.
*
*     In most cases of interest, however, this function will either
*     attempt to replace the nominated SpecMap with one which it
*     considers simpler, or to merge it with the Mappings which
*     immediately precede it or follow it in the sequence (both will
*     normally be considered). This is sufficient to ensure the
*     eventual simplification of most Mapping sequences by repeated
*     application of this function.
*
*     In some cases, the function may attempt more elaborate
*     simplification, involving any number of other Mappings in the
*     sequence. It is not restricted in the type or scope of
*     simplification it may perform, but will normally only attempt
*     elaborate simplification in cases where a more straightforward
*     approach is not adequate.

*  Parameters:
*     this
*        Pointer to the nominated SpecMap which is to be merged with
*        its neighbours. This should be a cloned copy of the SpecMap
*        pointer contained in the array element "(*map_list)[where]"
*        (see below). This pointer will not be annulled, and the
*        SpecMap it identifies will not be modified by this function.
*     where
*        Index in the "*map_list" array (below) at which the pointer
*        to the nominated SpecMap resides.
*     series
*        A non-zero value indicates that the sequence of Mappings to
*        be simplified will be applied in series (i.e. one after the
*        other), whereas a zero value indicates that they will be
*        applied in parallel (i.e. on successive sub-sets of the
*        input/output coordinates).
*     nmap
*        Address of an int which counts the number of Mappings in the
*        sequence. On entry this should be set to the initial number
*        of Mappings. On exit it will be updated to record the number
*        of Mappings remaining after simplification.
*     map_list
*        Address of a pointer to a dynamically allocated array of
*        Mapping pointers (produced, for example, by the astMapList
*        method) which identifies the sequence of Mappings. On entry,
*        the initial sequence of Mappings to be simplified should be
*        supplied.
*
*        On exit, the contents of this array will be modified to
*        reflect any simplification carried out. Any form of
*        simplification may be performed. This may involve any of: (a)
*        removing Mappings by annulling any of the pointers supplied,
*        (b) replacing them with pointers to new Mappings, (c)
*        inserting additional Mappings and (d) changing their order.
*
*        The intention is to reduce the number of Mappings in the
*        sequence, if possible, and any reduction will be reflected in
*        the value of "*nmap" returned. However, simplifications which
*        do not reduce the length of the sequence (but improve its
*        execution time, for example) may also be performed, and the
*        sequence might conceivably increase in length (but normally
*        only in order to split up a Mapping into pieces that can be
*        more easily merged with their neighbours on subsequent
*        invocations of this function).
*
*        If Mappings are removed from the sequence, any gaps that
*        remain will be closed up, by moving subsequent Mapping
*        pointers along in the array, so that vacated elements occur
*        at the end. If the sequence increases in length, the array
*        will be extended (and its pointer updated) if necessary to
*        accommodate any new elements.
*
*        Note that any (or all) of the Mapping pointers supplied in
*        this array may be annulled by this function, but the Mappings
*        to which they refer are not modified in any way (although
*        they may, of course, be deleted if the annulled pointer is
*        the final one).
*     invert_list
*        Address of a pointer to a dynamically allocated array which,
*        on entry, should contain values to be assigned to the Invert
*        attributes of the Mappings identified in the "*map_list"
*        array before they are applied (this array might have been
*        produced, for example, by the astMapList method). These
*        values will be used by this function instead of the actual
*        Invert attributes of the Mappings supplied, which are
*        ignored.
*
*        On exit, the contents of this array will be updated to
*        correspond with the possibly modified contents of the
*        "*map_list" array.  If the Mapping sequence increases in
*        length, the "*invert_list" array will be extended (and its
*        pointer updated) if necessary to accommodate any new
*        elements.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     If simplification was possible, the function returns the index
*     in the "map_list" array of the first element which was
*     modified. Otherwise, it returns -1 (and makes no changes to the
*     arrays supplied).

*  Notes:
*     - A value of -1 will be returned if this function is invoked
*     with the global error status set, or if it should fail for any
*     reason.
*/

/* Local Variables: */
   AstMapping *new;              /* Pointer to replacement Mapping */
   AstSpecMap *specmap;            /* Pointer to SpecMap */
   const char *argdesc[ MAX_ARGS ]; /* Argument descriptions (junk) */
   const char *class;            /* Pointer to Mapping class string */
   const char *comment;          /* Pointer to comment string (junk) */
   double (*cvtargs)[ MAX_ARGS ]; /* Pointer to argument arrays */
   double tmp;                   /* Temporary storage */
   int *cvttype;                 /* Pointer to transformation type codes */
   int *narg;                    /* Pointer to argument count */
   int *szarg;                   /* Pointer to argument array size */
   int argdec;                   /* Index of DEC argument */
   int argra;                    /* Index of RA argument */
   int done;                     /* Finished (no further simplification)? */
   int iarg;                     /* Loop counter for arguments */
   int icvt1;                    /* Loop initial value */
   int icvt2;                    /* Loop final value */
   int icvt;                     /* Loop counter for transformation steps */
   int ikeep;                    /* Index to store step being kept */
   int imap1;                    /* Index of first SpecMap to merge */
   int imap2;                    /* Index of last SpecMap to merge */
   int imap;                     /* Loop counter for Mappings */
   int inc;                      /* Increment for transformation step loop */
   int invert;                   /* SpecMap applied in inverse direction? */
   int istep;                    /* Loop counter for transformation steps */
   int keep;                     /* Keep transformation step? */
   int ngone;                    /* Number of Mappings eliminated */
   int nin;                      /* Numbr of axes for SpecMaps being merged */
   int nstep0;                   /* Original number of transformation steps */
   int nstep;                    /* Total number of transformation steps */
   int result;                   /* Result value to return */
   int simpler;                  /* Simplification possible? */
   int unit;                     /* Replacement Mapping is a UnitMap? */

/* Initialise. */
   result = -1;

/* Check the global error status. */
   if ( !astOK ) return result;

/* SpecMaps can only be merged if they are in series (or if there is
   only one Mapping present, in which case it makes no difference), so
   do nothing if they are not. */
   if ( series || ( *nmap == 1 ) ) {

/* Save the number of inputs for the SpecMap. */
      nin = astGetNin( this );

/* Initialise the number of transformation steps to be merged to equal
   the number in the nominated SpecMap. */
      nstep = ( (AstSpecMap *) ( *map_list )[ where ] )->ncvt;

/* Search adjacent lower-numbered Mappings until one is found which is
   not a SpecMap, or is a SpecMap with a different number of axes. Accumulate
   the number of transformation steps involved in any SpecMaps found. */
      imap1 = where;
      while ( ( imap1 - 1 >= 0 ) && astOK ) {
         class = astGetClass( ( *map_list )[ imap1 - 1 ] );
         if ( !astOK || strcmp( class, "SpecMap" ) ||
              astGetNin( ( *map_list )[ imap1 - 1 ] ) != nin ) break;
         nstep += ( (AstSpecMap *) ( *map_list )[ imap1 - 1 ] )->ncvt;
         imap1--;
      }

/* Similarly search adjacent higher-numbered Mappings. */
      imap2 = where;
      while ( ( imap2 + 1 < *nmap ) && astOK ) {
         class = astGetClass( ( *map_list )[ imap2 + 1 ] );
         if ( !astOK || strcmp( class, "SpecMap" ) ||
              astGetNin( ( *map_list )[ imap2 + 1 ] ) != nin ) break;
         nstep += ( (AstSpecMap *) ( *map_list )[ imap2 + 1 ] )->ncvt;
         imap2++;
      }

/* Remember the initial number of transformation steps. */
      nstep0 = nstep;

/* Allocate memory for accumulating a list of all the transformation
   steps involved in all the SpecMaps found. */
      cvttype = astMalloc( sizeof( int ) * (size_t) nstep );
      cvtargs = astMalloc( sizeof( double[ MAX_ARGS ] ) * (size_t) nstep );
      szarg = astMalloc( sizeof( int ) * (size_t) nstep );
      narg = astMalloc( sizeof( int ) * (size_t) nstep );

/* Loop to obtain the transformation data for each SpecMap being merged. */
      nstep = 0;
      for ( imap = imap1; astOK && ( imap <= imap2 ); imap++ ) {

/* Obtain a pointer to the SpecMap and note if it is being applied in
   its inverse direction. */
         specmap = (AstSpecMap *) ( *map_list )[ imap ];
         invert = ( *invert_list )[ imap ];

/* Set up loop limits and an increment to scan the transformation
   steps in each SpecMap in either the forward or reverse direction, as
   dictated by the associated "invert" value. */
         icvt1 = invert ? specmap->ncvt - 1 : 0;
         icvt2 = invert ? -1 : specmap->ncvt;
         inc = invert ? -1 : 1;

/* Loop through each transformation step in the SpecMap. */
         for ( icvt = icvt1; icvt != icvt2; icvt += inc ) {

/* Store the transformation type code and use "CvtString" to determine
   the associated number of arguments. Then store these arguments. */
            cvttype[ nstep ] = specmap->cvttype[ icvt ];
            (void) CvtString( cvttype[ nstep ], &comment, &argra, &argdec,
                              narg + nstep, szarg + nstep, argdesc, status );
            if ( !astOK ) break;
            for ( iarg = 0; iarg < szarg[ nstep ]; iarg++ ) {
               cvtargs[ nstep ][ iarg ] = specmap->cvtargs[ icvt ][ iarg ];
            }

/* If the SpecMap is inverted, we must not only accumulate its
   transformation steps in reverse, but also apply them in
   reverse. For some steps this means changing arguments, for some it
   means changing the transformation type code to a complementary
   value, and for others it means both.  Define macros to perform each
   of the required changes. */

/* Macro to exchange a transformation type code for its inverse (and
   vice versa). */
#define SWAP_CODES( code1, code2 ) \
            if ( cvttype[ nstep ] == code1 ) { \
               cvttype[ nstep ] = code2; \
            } else if ( cvttype[ nstep ] == code2 ) { \
               cvttype[ nstep ] = code1; \
            }

/* Macro to exchange a transformation type code for its inverse (and
   vice versa), and reciprocate a specified argument. */
#define SWAP_CODES2( code1, code2, jarg ) \
            if ( cvttype[ nstep ] == code1 ) { \
               cvttype[ nstep ] = code2; \
               tmp = cvtargs[ nstep ][ jarg ]; \
               if( tmp != AST__BAD && tmp != 0.0 ) { \
                  cvtargs[ nstep ][ jarg ] = 1.0/tmp; \
               } else { \
                  cvtargs[ nstep ][ jarg ] = AST__BAD; \
               } \
            } else if ( cvttype[ nstep ] == code2 ) { \
               cvttype[ nstep ] = code1; \
               tmp = cvtargs[ nstep ][ jarg ]; \
               if( tmp != AST__BAD && tmp != 0.0 ) { \
                  cvtargs[ nstep ][ jarg ] = 1.0/tmp; \
               } else { \
                  cvtargs[ nstep ][ jarg ] = AST__BAD; \
               } \
            }

/* Macro to exchange a transformation type code for its inverse (and
   vice versa), and negate a specified argument. */
#define SWAP_CODES3( code1, code2, jarg ) \
            if ( cvttype[ nstep ] == code1 ) { \
               cvttype[ nstep ] = code2; \
               tmp = cvtargs[ nstep ][ jarg ]; \
               if( tmp != AST__BAD ) { \
                  cvtargs[ nstep ][ jarg ] = -tmp; \
               } \
            } else if ( cvttype[ nstep ] == code2 ) { \
               cvttype[ nstep ] = code1; \
               tmp = cvtargs[ nstep ][ jarg ]; \
               if( tmp != AST__BAD ) { \
                  cvtargs[ nstep ][ jarg ] = -tmp; \
               } \
            }

/* Use these macros to apply the changes where needed. */
            if ( invert ) {

/* Exchange transformation codes for their inverses. */
               SWAP_CODES( AST__FRTOVL, AST__VLTOFR )
               SWAP_CODES( AST__ENTOFR, AST__FRTOEN )
               SWAP_CODES( AST__WNTOFR, AST__FRTOWN )
               SWAP_CODES( AST__WVTOFR, AST__FRTOWV )
               SWAP_CODES( AST__AWTOFR, AST__FRTOAW )
               SWAP_CODES( AST__VRTOVL, AST__VLTOVR )
               SWAP_CODES( AST__VOTOVL, AST__VLTOVO )
               SWAP_CODES( AST__ZOTOVL, AST__VLTOZO )
               SWAP_CODES( AST__BTTOVL, AST__VLTOBT )

/* Exchange transformation codes for their inverses, and reciprocate the
   frequency correction factor. */
               SWAP_CODES2( AST__TPF2HL, AST__HLF2TP, 6 )
               SWAP_CODES2( AST__USF2HL, AST__HLF2US, 3 )
               SWAP_CODES2( AST__GEF2HL, AST__HLF2GE, 3 )
               SWAP_CODES2( AST__BYF2HL, AST__HLF2BY, 3 )
               SWAP_CODES2( AST__LKF2HL, AST__HLF2LK, 2 )
               SWAP_CODES2( AST__LDF2HL, AST__HLF2LD, 2 )
               SWAP_CODES2( AST__LGF2HL, AST__HLF2LG, 2 )
               SWAP_CODES2( AST__GLF2HL, AST__HLF2GL, 2 )

            }

/* Undefine the local macros. */
#undef SWAP_CODES
#undef SWAP_CODES2
#undef SWAP_CODES3

/* Count the transformation steps. */
            nstep++;
         }
      }

/* Loop to simplify the sequence of transformation steps until no
   further improvement is possible. */
      done = 0;
      while ( astOK && !done ) {

/* Examine each remaining transformation step in turn.  */
         ikeep = -1;
         for ( istep = 0; istep < nstep; istep++ ) {

/* Initially assume we will retain the current step. */
            keep = 1;

/* The only simplifications for the conversions currently in this class act
   to combine adjacent transformation steps, so only apply them while there
   are at least 2 steps left. */
            if ( istep < ( nstep - 1 ) ) {

/* Define a macro to test if two adjacent transformation type codes
   have specified values. */
#define PAIR_CVT( code1, code2 ) \
               ( ( cvttype[ istep ] == code1 ) && \
                 ( cvttype[ istep + 1 ] == code2 ) )

/* Define a macro to test if two adjacent transformation type codes
   have specified values, either way round. */
#define PAIR_CVT2( code1, code2 ) \
               ( ( PAIR_CVT( code1, code2 ) ) || \
                 ( PAIR_CVT( code2, code1 ) ) )

/* If a correction is followed by its inverse, and the user-supplied argument
   values are unchanged (we do not need to test values stored in the
   argument array which were not supplied by the user), we can eliminate them.
   First check for conversions which have no user-supplied arguments. */
               if ( PAIR_CVT2( AST__ENTOFR, AST__FRTOEN ) ||
                    PAIR_CVT2( AST__WNTOFR, AST__FRTOWN ) ||
                    PAIR_CVT2( AST__WVTOFR, AST__FRTOWV ) ||
                    PAIR_CVT2( AST__AWTOFR, AST__FRTOAW ) ||
                    PAIR_CVT2( AST__VRTOVL, AST__VLTOVR ) ||
                    PAIR_CVT2( AST__VOTOVL, AST__VLTOVO ) ||
                    PAIR_CVT2( AST__ZOTOVL, AST__VLTOZO ) ||
                    PAIR_CVT2( AST__BTTOVL, AST__VLTOBT ) ) {
                  istep++;
                  keep = 0;

/* Now check for conversions which have a single user-supplied argument. */
               } else if( PAIR_CVT2( AST__FRTOVL, AST__VLTOFR ) &&
                          astEQUAL( cvtargs[ istep ][ 0 ],
                                 cvtargs[ istep + 1 ][ 0 ] ) ) {
                  istep++;
                  keep = 0;

/* Now check for conversions which have two user-supplied arguments. */
               } else if( ( PAIR_CVT2( AST__LKF2HL, AST__HLF2LK ) ||
                            PAIR_CVT2( AST__LDF2HL, AST__HLF2LD ) ||
                            PAIR_CVT2( AST__LGF2HL, AST__HLF2LG ) ||
                            PAIR_CVT2( AST__GLF2HL, AST__HLF2GL ) ) &&
                          astEQUAL( cvtargs[ istep ][ 0 ],
                                 cvtargs[ istep + 1 ][ 0 ] ) &&
                          astEQUAL( cvtargs[ istep ][ 1 ],
                                 cvtargs[ istep + 1 ][ 1 ] ) ) {
                  istep++;
                  keep = 0;

/* Now check for conversions which have three user-supplied arguments. */
               } else if( ( PAIR_CVT2( AST__GEF2HL, AST__HLF2GE ) ||
                            PAIR_CVT2( AST__BYF2HL, AST__HLF2BY ) ||
                            PAIR_CVT2( AST__USF2HL, AST__HLF2US ) ) &&
                          astEQUAL( cvtargs[ istep ][ 0 ],
                                 cvtargs[ istep + 1 ][ 0 ] ) &&
                          astEQUAL( cvtargs[ istep ][ 1 ],
                                 cvtargs[ istep + 1 ][ 1 ] ) &&
                          astEQUAL( cvtargs[ istep ][ 2 ],
                                 cvtargs[ istep + 1 ][ 2 ] ) ) {
                  istep++;
                  keep = 0;

/* Now check for conversions which have six user-supplied arguments (currently
   no conversions have four or five user-supplied arguments). */
               } else if( ( PAIR_CVT2( AST__TPF2HL, AST__HLF2TP ) ) &&
                          astEQUAL( cvtargs[ istep ][ 0 ],
                                 cvtargs[ istep + 1 ][ 0 ] ) &&
                          astEQUAL( cvtargs[ istep ][ 1 ],
                                 cvtargs[ istep + 1 ][ 1 ] ) &&
                          astEQUAL( cvtargs[ istep ][ 2 ],
                                 cvtargs[ istep + 1 ][ 2 ] ) &&
                          astEQUAL( cvtargs[ istep ][ 3 ],
                                 cvtargs[ istep + 1 ][ 3 ] ) &&
                          astEQUAL( cvtargs[ istep ][ 4 ],
                                 cvtargs[ istep + 1 ][ 4 ] ) &&
                          astEQUAL( cvtargs[ istep ][ 5 ],
                                 cvtargs[ istep + 1 ][ 5 ] ) ) {
                  istep++;
                  keep = 0;

               }

/* Undefine the local macros. */
#undef PAIR_CVT
#undef PAIR_CVT2
            }

/* If the current transformation (possibly modified above) is being
   kept, then increment the index that identifies its new location in
   the list of transformation steps. */
            if ( keep ) {
               ikeep++;

/* If the new location is different to its current location, copy the
   transformation data into the new location. */
               if ( ikeep != istep ) {
                  cvttype[ ikeep ] = cvttype[ istep ];
                  for ( iarg = 0; iarg < szarg[ istep ]; iarg++ ) {
                     cvtargs[ ikeep ][ iarg ] = cvtargs[ istep ][ iarg ];
                  }
                  szarg[ ikeep ] = szarg[ istep ];
                  narg[ ikeep ] = narg[ istep ];
               }
            }
         }

/* Note if no simplification was achieved on this iteration (i.e. the
   number of transformation steps was not reduced). This is the signal
   to quit. */
         done = ( ( ikeep + 1 ) >= nstep );

/* Note how many transformation steps now remain. */
         nstep = ikeep + 1;
      }

/* Determine how many Mappings can be eliminated by condensing all
   those considered above into a single Mapping. */
      if ( astOK ) {
         ngone = imap2 - imap1;

/* Determine if the replacement Mapping can be a UnitMap (a null
   Mapping). This will only be the case if all the transformation
   steps were eliminated above. */
         unit = ( nstep == 0 );

/* Determine if simplification is possible. This will be the case if
   (a) Mappings were eliminated ("ngone" is non-zero), or (b) the
   number of transformation steps was reduced, or (c) the SpecMap(s)
   can be replaced by a UnitMap, or (d) if there was initially only
   one SpecMap present, its invert flag was set (this flag will always
   be cleared in the replacement Mapping). */
         simpler = ngone || ( nstep < nstep0 ) || unit ||
                   ( *invert_list )[ where ];

/* Do nothing more unless simplification is possible. */
         if ( simpler ) {

/* If the replacement Mapping is a UnitMap, then create it. */
            if ( unit ) {
               new = (AstMapping *)
                        astUnitMap( astGetNin( ( *map_list )[ where ] ), "", status );

/* Otherwise, create a replacement SpecMap and add each of the
   remaining transformation steps to it. */
            } else {
               new = (AstMapping *) astSpecMap( nin, 0, "", status );
               for ( istep = 0; istep < nstep; istep++ ) {
                  AddSpecCvt( (AstSpecMap *) new, cvttype[ istep ],
                             narg[ istep ], cvtargs[ istep ], status );
               }
            }

/* Annul the pointers to the Mappings being eliminated. */
            if ( astOK ) {
               for ( imap = imap1; imap <= imap2; imap++ ) {
                  ( *map_list )[ imap ] = astAnnul( ( *map_list )[ imap ] );
               }

/* Insert the pointer and invert value for the new Mapping. */
               ( *map_list )[ imap1 ] = new;
               ( *invert_list )[ imap1 ] = 0;

/* Move any subsequent Mapping information down to close the gap. */
               for ( imap = imap2 + 1; imap < *nmap; imap++ ) {
                  ( *map_list )[ imap - ngone ] = ( *map_list )[ imap ];
                  ( *invert_list )[ imap - ngone ] = ( *invert_list )[ imap ];
               }

/* Blank out any information remaining at the end of the arrays. */
               for ( imap = ( *nmap - ngone ); imap < *nmap; imap++ ) {
                  ( *map_list )[ imap ] = NULL;
                  ( *invert_list )[ imap ] = 0;
               }

/* Decrement the Mapping count and return the index of the first
   Mapping which was eliminated. */
               ( *nmap ) -= ngone;
               result = imap1;

/* If an error occurred, annul the new Mapping pointer. */
            } else {
               new = astAnnul( new );
            }
         }
      }

/* Free the memory used for the transformation steps. */
      cvttype = astFree( cvttype );
      cvtargs = astFree( cvtargs );
      szarg = astFree( szarg );
      narg = astFree( narg );
   }

/* If an error occurred, clear the returned value. */
   if ( !astOK ) result = -1;

/* Return the result. */
   return result;
}

static double Rate( AstMapping *this, double *at, int ax1, int ax2, int *status ){
/*
*  Name:
*     Rate

*  Purpose:
*     Calculate the rate of change of a Mapping output.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     result = Rate( AstMapping *this, double *at, int ax1, int ax2, int *status )

*  Class Membership:
*     SpecMap member function (overrides the astRate method inherited
*     from the Mapping class ).

*  Description:
*     This function returns the rate of change of a specified output of
*     the supplied Mapping with respect to a specified input, at a
*     specified input position.

*  Parameters:
*     this
*        Pointer to the Mapping to be applied.
*     at
*        The address of an array holding the axis values at the position
*        at which the rate of change is to be evaluated. The number of
*        elements in this array should equal the number of inputs to the
*        Mapping.
*     ax1
*        The index of the Mapping output for which the rate of change is to
*        be found (output numbering starts at 0 for the first output).
*     ax2
*        The index of the Mapping input which is to be varied in order to
*        find the rate of change (input numbering starts at 0 for the first
*        input).
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     The rate of change of Mapping output "ax1" with respect to input
*     "ax2", evaluated at "at", or AST__BAD if the value cannot be
*     calculated.

*  Implementation Deficiencies:
*     The initial version of this implementation only deals with
*     frequency->wavelength conversions. This is because the slowness of
*     the numerical differentiation implemented by the astRate method in
*     the parent Mapping class is cripples conversion between SpecFluxFrames.
*     Such conversions only rely on rate of change of wavelength with
*     respect to frequency. This implementation should be extended when
*     needed.

*/

/* Local Variables: */
   AstSpecMap *map;
   double result;
   int cvt;

/* Check inherited status */
   if( !astOK ) return AST__BAD;

/* Get a pointer to the SpecMap structure. */
   map = (AstSpecMap *) this;

/* Return 1.0 if the SpecMap has no conversions. */
   if( map->ncvt == 0 ) return 1.0;

/* Store the type of the first conversion.*/
   cvt = map->cvttype[ 0 ];

/* If this is a 3D SpecMap or if it has more than one component, or if
   that conversion is not between frequency and wavelength, use the
   astRate method inherited form the parent Mapping class. */
   if( astGetNin( map ) != 1 || map->ncvt != 1 ||
       ( cvt != AST__WVTOFR && cvt != AST__FRTOWV ) ) {
      result = (*parent_rate)( this, at, ax1, ax2, status );

/* Otherwise, evaluate the known analytical expressions for the rate of
   change of frequency with respect to wavelength or wavelength with
   respect to frequency. */
   } else {
      result = ( *at != AST__BAD ) ? -AST__C/((*at)*(*at)) : AST__BAD;
   }

/* Return the result. */
   return result;
}

static double Refrac( double wavelen, int *status ){
/*
*  Name:
*     Refrac

*  Purpose:
*     Returns the refractive index of dry air at a given wavelength.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     double Refrac( double wavelen, int *status )

*  Class Membership:
*     SpecMap method.

*  Description:
*     This function returns the refractive index of dry air at standard
*     temperature and pressure, at a given wavelength. The formula is
*     taken from the paper "Representation of Spectral Coordinates in FITS"
*     (Greisen et al).

*  Parameters:
*     wavelen
*        The wavelength, in metres. This should be the air wavelength,
*        but supplying the vacuum wavelength will make no significant
*        difference.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     The refractive index. A value of 1.0 is returned if an error
*     occurs, or has already occurred.

*/

/* Local Variables: */
   double w2;                /* Wavenumber squared */

/* Check the global error status. */
   if ( !astOK || wavelen == 0.0 ) return 1.0;

/* Find the squared wave number in units of "(per um)**2". */
   w2 = 1.0E-12/( wavelen * wavelen );

/* Apply the rest of the algorithm as described in the FITS WCS
   paper III. */
   return 1.0 + 1.0E-6*( 287.6155 + 1.62887*w2 + 0.01360*w2*w2 );
}

static double Rverot( double phi, double h, double ra, double da,
                      double st, int *status ) {
/*
*  Name:
*     Rverot

*  Purpose:
*     Find the velocity component in a given direction due to Earth rotation.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     double Rverot( double phi, double h, double ra, double da,
*                    double st, int *status )

*  Class Membership:
*     SpecMap method.

*  Description:
*     This function is like slaRverot, except that it takes account of the
*     observers height (h), and does all calculations in double precision.

*  Parameters:
*     phi
*        The geodetic latitude of the observer (radians, IAU 1976).
*     h
*        The geodetic height above the reference spheroid of the observer
*        (metres, IAU 1976).
*     ra
*        The geocentric apparent RA (rads) of the source.
*     da
*        The geocentric apparent Dec (rads) of the source.
*     st
*        The local apparent sidereal time (radians).
*     status
*        Pointer to the inherited status variable.

*  Returns:
*     The component of the Earth rotation in direction [RA,DA] (km/s).
*     The result is positive when the observer is receding from the
*     given point on the sky. Zero is returned if an error has already
*     occurred.

*/

/* Local Variables: */
   double pv[ 6 ];           /* Observer position and velocity */
   double v[ 3 ];            /* Source direction vector */

/* Check the global error status. */
   if ( !astOK ) return 0.0;

/* Get the Cartesian coordinates of the unit vector pointing towards the
   given sky position. */
   palDcs2c( ra, da, v );

/* Get velocity and position of the observer. */
   palPvobs( phi, h, st, pv );

/* Return the component of the observer's velocity away from the sky
   position, and convert from AU/s to km/s. */
   return -palDvdv( v, pv + 3 )*149.597870E6;
}

static void SpecAdd( AstSpecMap *this, const char *cvt, int narg,
                     const double args[], int *status ) {
/*
*++
*  Name:
c     astSpecAdd
f     AST_SPECADD

*  Purpose:
*     Add a spectral coordinate conversion to a SpecMap.

*  Type:
*     Public virtual function.

*  Synopsis:
c     #include "specmap.h"
c     void astSpecAdd( AstSpecMap *this, const char *cvt, int narg,
c                      const double args[] )
f     CALL AST_SPECADD( THIS, CVT, NARG, ARGS, STATUS )

*  Class Membership:
*     SpecMap method.

*  Description:
c     This function adds one of the standard spectral coordinate
f     This routine adds one of the standard spectral coordinate
*     system conversions listed below to an existing SpecMap.
*
c     When a SpecMap is first created (using astSpecMap), it simply
f     When a SpecMap is first created (using AST_SPECMAP), it simply
c     performs a unit (null) Mapping. By using astSpecAdd (repeatedly
f     performs a unit (null) Mapping. By using AST_SPECADD (repeatedly
*     if necessary), one or more coordinate conversion steps may then
*     be added, which the SpecMap will perform in sequence. This allows
*     multi-step conversions between a variety of spectral coordinate
*     systems to be assembled out of the building blocks provided by
*     this class.
*
*     Normally, if a SpecMap's Invert attribute is zero (the default),
*     then its forward transformation is performed by carrying out
*     each of the individual coordinate conversions specified by
c     astSpecAdd in the order given (i.e. with the most recently added
f     AST_SPECADD in the order given (i.e. with the most recently added
*     conversion applied last).
*
*     This order is reversed if the SpecMap's Invert attribute is
*     non-zero (or if the inverse transformation is requested by any
*     other means) and each individual coordinate conversion is also
*     replaced by its own inverse. This process inverts the overall
*     effect of the SpecMap. In this case, the first conversion to be
*     applied would be the inverse of the one most recently added.

*  Parameters:
c     this
f     THIS = INTEGER (Given)
*        Pointer to the SpecMap.
c     cvt
f     CVT = CHARACTER * ( * ) (Given)
c        Pointer to a null-terminated string which identifies the
f        A character string which identifies the
*        spectral coordinate conversion to be added to the
*        SpecMap. See the "Available Conversions" section for details of
*        those available.
c     narg
f     NARG = INTEGER (Given)
*        The number of argument values supplied in the
c        "args" array.
f        ARGS array.
c     args
f     ARGS( * ) = DOUBLE PRECISION (Given)
*        An array containing argument values for the spectral
*        coordinate conversion. The number of arguments required, and
*        hence the number of array elements used, depends on the
*        conversion specified (see the "Available Conversions"
*        section). This array is ignored
c        and a NULL pointer may be supplied
*        if no arguments are needed.
f     STATUS = INTEGER (Given and Returned)
f        The global status.

*  Notes:
*     - When assembling a multi-stage conversion, it can sometimes be
*     difficult to determine the most economical conversion path. For
*     example, when converting between reference frames, converting first
*     to the heliographic reference frame as an intermediate stage is often
*     sensible in formulating the problem, but may introduce unnecessary
*     extra conversion steps. A solution to this is to include all the steps
*     which are (logically) necessary, but then to use
c     astSimplify to simplify the resulting
f     AST_SIMPLIFY to simplify the resulting
*     SpecMap. The simplification process will eliminate any steps
*     which turn out not to be needed.
c     - This function does not check to ensure that the sequence of
f     - This routine does not check to ensure that the sequence of
*     coordinate conversions added to a SpecMap is physically
*     meaningful.

*  Available Conversions:
*     The following strings (which are case-insensitive) may be supplied
c     via the "cvt" parameter to indicate which spectral coordinate
f     via the CVT argument to indicate which spectral coordinate
*     conversion is to be added to the SpecMap. Where arguments are needed by
*     the conversion, they are listed in parentheses. Values for
c     these arguments should be given, via the "args" array, in the
f     these arguments should be given, via the ARGS array, in the
*     order indicated. Units and argument names are described at the end of
*     the list of conversions.

*     - "FRTOVL" (RF): Convert frequency to relativistic velocity.
*     - "VLTOFR" (RF): Convert relativistic velocity to Frequency.
*     - "ENTOFR": Convert energy to frequency.
*     - "FRTOEN": Convert frequency to energy.
*     - "WNTOFR": Convert wave number to frequency.
*     - "FRTOWN": Convert frequency to wave number.
*     - "WVTOFR": Convert wavelength (vacuum) to frequency.
*     - "FRTOWV": Convert frequency to wavelength (vacuum).
*     - "AWTOFR": Convert wavelength (air) to frequency.
*     - "FRTOAW": Convert frequency to wavelength (air).
*     - "VRTOVL": Convert radio to relativistic velocity.
*     - "VLTOVR": Convert relativistic to radio velocity.
*     - "VOTOVL": Convert optical to relativistic velocity.
*     - "VLTOVO": Convert relativistic to optical velocity.
*     - "ZOTOVL": Convert redshift to relativistic velocity.
*     - "VLTOZO": Convert relativistic velocity to redshift.
*     - "BTTOVL": Convert beta factor to relativistic velocity.
*     - "VLTOBT": Convert relativistic velocity to beta factor.
*     - "USF2HL" (VOFF,RA,DEC): Convert frequency from a user-defined
*     reference frame to heliocentric.
*     - "HLF2US" (VOFF,RA,DEC): Convert frequency from heliocentric
*     reference frame to user-defined.
*     - "TPF2HL" (OBSLON,OBSLAT,OBSALT,EPOCH,RA,DEC): Convert frequency from
*     topocentric reference frame to heliocentric.
*     - "HLF2TP" (OBSLON,OBSLAT,OBSALT,EPOCH,RA,DEC): Convert frequency from
*     heliocentric reference frame to topocentric.
*     - "GEF2HL" (EPOCH,RA,DEC): Convert frequency from geocentric
*     reference frame to heliocentric.
*     - "HLF2GE" (EPOCH,RA,DEC): Convert frequency from
*     heliocentric reference frame to geocentric.
*     - "BYF2HL" (EPOCH,RA,DEC): Convert frequency from
*     barycentric reference frame to heliocentric.
*     - "HLF2BY" (EPOCH,RA,DEC): Convert frequency from
*     heliocentric reference frame to barycentric.
*     - "LKF2HL" (RA,DEC): Convert frequency from kinematic LSR
*     reference frame to heliocentric.
*     - "HLF2LK" (RA,DEC): Convert frequency from heliocentric
*     reference frame to kinematic LSR.
*     - "LDF2HL" (RA,DEC): Convert frequency from dynamical LSR
*     reference frame to heliocentric.
*     - "HLF2LD" (RA,DEC): Convert frequency from heliocentric
*     reference frame to dynamical LSR.
*     - "LGF2HL" (RA,DEC): Convert frequency from local group
*     reference frame to heliocentric.
*     - "HLF2LG" (RA,DEC): Convert frequency from heliocentric
*     reference frame to local group.
*     - "GLF2HL" (RA,DEC): Convert frequency from galactic
*     reference frame to heliocentric.
*     - "HLF2GL" (RA,DEC): Convert frequency from heliocentric
*     reference frame to galactic.

*     The units for the values processed by the above conversions are as
*     follows:
*
*     - all velocities: metres per second (positive if the source receeds from
*       the observer).
*     - frequency: Hertz.
*     - all wavelengths: metres.
*     - energy: Joules.
*     - wave number: cycles per metre.
*
*     The arguments used in the above conversions are as follows:
*
*     - RF: Rest frequency (Hz).
*     - OBSALT: Geodetic altitude of observer (IAU 1975, metres).
*     - OBSLAT: Geodetic latitude of observer (IAU 1975, radians).
*     - OBSLON: Longitude of observer (radians - positive eastwards).
*     - EPOCH: Epoch of observation (UT1 expressed as a Modified Julian Date).
*     - RA: Right Ascension of source (radians, FK5 J2000).
*     - DEC: Declination of source (radians, FK5 J2000).
*     - VOFF: Velocity of the user-defined reference frame, towards the
*     position given by RA and DEC, measured in the heliocentric
*     reference frame.
*
*     If the SpecMap is 3-dimensional, source positions are provided by the
*     values supplied to inputs 2 and 3 of the SpecMap (which are simply
*     copied to outputs 2 and 3). Note, usable values are still required
*     for the RA and DEC arguments in order to define the "user-defined"
*     reference frame used by USF2HL and HLF2US. However, AST__BAD can be
*     supplied for RA and DEC if the user-defined reference frame is not
*     required.
*
*--
*/

/* Local Variables: */
   int cvttype;                  /* Conversion type code */

/* Check the inherited status. */
   if ( !astOK ) return;

/* Validate the type string supplied and obtain the equivalent
   conversion type code. */
   cvttype = CvtCode( cvt, status );

/* If the string was not recognised, then report an error. */
   if ( astOK && ( cvttype == AST__SPEC_NULL ) ) {
      astError( AST__SPCIN,
                "%s(%s): Invalid SpecMap spectral coordinate "
                "conversion type \"%s\".", status, "astAddSpec", astGetClass( this ), cvt );
   }

/* Add the new conversion to the SpecMap. */
   AddSpecCvt( this, cvttype, narg, args, status );
}

static int SystemChange( int cvt_code, int np, double *values, double *args,
                         int forward, int *status ){
/*
*  Name:
*     SystemChange

*  Purpose:
*     Change values between two spectral systems.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     int SystemChange( int cvt_code, int np, double *values, double *args,
*                       int forward, int *status )

*  Class Membership:
*     SpecMap method.

*  Description:
*     This function modifies the supplied values in order to change the
*     spectral co-ordinate system (frequency, wavelength, etc) to which
*     they refer.

*  Parameters:
*     cvt_code
*        A code indicating the conversion to be applied. If the code does
*        not correspond to a change of system, then the supplied values
*        are left unchanged and zero is returned as the function value.
*     np
*        The number of frequency values to transform.
*     values
*        Pointer to an array of "np" spectral values. These are modified on
*        return to hold the corresponding values measured in the output
*        system.
*     args
*        Pointer to an array holding the conversion arguments. The number
*        of arguments expected depends on the particular conversion being
*        used.
*     forward
*        Should the conversion be applied in the forward or inverse
*        direction? Non-zero for forward, zero for inverse.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     Non-zero if the supplied conversion code corresponds to a change of
*     system. Zero otherwise  (in which case the upplied values will not
*     have been changed).

*/

/* Local Variables: */
   double *pv;        /* Pointer to next value */
   double d;          /* Intermediate value */
   double f2;         /* Squared frequency */
   double temp;       /* Intermediate value */
   int i;             /* Loop index */
   int iter;          /* Iteration count */
   int result;        /* Returned value */

/* Check inherited status. */
   if( !astOK ) return 0;

/* Set the return value to indicate that the supplied conversion code
   represents a change of system. */
   result = 1;

/* Test for each code value in turn and assign the appropriate values. */
   switch ( cvt_code ) {

/* Frequency to relativistic velocity. */
   case AST__FRTOVL:
      if( forward ) {
         if( args[ 0 ] != AST__BAD ) {
            temp = args[ 0 ] * args[ 0 ];
            pv = values - 1;
            for( i = 0; i < np; i++ ){
               pv++;
               if( *pv != AST__BAD ) {
                  f2 = ( *pv ) * ( *pv );
                  d = temp + f2;
                  if( d > 0.0 ) {
                     *pv = AST__C*( ( temp - f2 )/d );
                     if( !astISFINITE( *pv ) ) *pv = AST__BAD;
                  } else {
                     *pv = AST__BAD;
                  }
               }
            }
         } else {
            pv = values;
            for( i = 0; i < np; i++ ) *( pv++ ) = AST__BAD;
         }
      } else {
         SystemChange( AST__VLTOFR, np, values, args, 1, status );
      }
      break;

/* Relativistic velocity to frequency. */
   case AST__VLTOFR:
      if( forward ) {
         if( args[ 0 ] != AST__BAD ) {
            temp = args[ 0 ];
            pv = values - 1;
            for( i = 0; i < np; i++ ){
               pv++;
               if( *pv != AST__BAD ) {
                  d = AST__C + ( *pv );
                  if( d != 0.0 ) {
                     d = ( AST__C - ( *pv ) )/d;
                     if( d >= 0.0 ) {
                        *pv = temp*sqrt( d );
                        if( !astISFINITE( *pv ) ) *pv = AST__BAD;
                     } else {
                        *pv = AST__BAD;
                     }
                  } else {
                     *pv = AST__BAD;
                  }
               }
            }
         } else {
            pv = values;
            for( i = 0; i < np; i++ ) *( pv++ ) = AST__BAD;
         }
      } else {
         SystemChange( AST__FRTOVL, np, values, args, 1, status );
      }
      break;

/* Energy to frequency */
   case AST__ENTOFR:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD ) {
               *pv /= AST__H;
            }
         }
      } else {
         SystemChange( AST__FRTOEN, np, values, args, 1, status );
      }
      break;

/* Frequency to energy */
   case AST__FRTOEN:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD ) {
               *pv *= AST__H;
            }
         }
      } else {
         SystemChange( AST__ENTOFR, np, values, args, 1, status );
      }
      break;

/* Wave number to frequency */
   case AST__WNTOFR:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD ) {
               *pv *= AST__C;
            }
         }
      } else {
         SystemChange( AST__FRTOWN, np, values, args, 1, status );
      }
      break;

/* Wave number to frequency */
   case AST__FRTOWN:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD ) {
               *pv /= AST__C;
            }
         }
      } else {
         SystemChange( AST__WNTOFR, np, values, args, 1, status );
      }
      break;

/* Wavelength to frequency */
   case AST__WVTOFR:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD && *pv != 0.0 ) {
               *pv = AST__C/( *pv );
               if( !astISFINITE( *pv ) ) *pv = AST__BAD;
            } else {
               *pv = AST__BAD;
            }
         }
      } else {
         SystemChange( AST__FRTOWV, np, values, args, 1, status );
      }
      break;

/* Frequency to wavelength. */
   case AST__FRTOWV:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD && *pv != 0.0 ) {
               *pv = AST__C/( *pv );
               if( !astISFINITE( *pv ) ) *pv = AST__BAD;
            } else {
               *pv = AST__BAD;
            }
         }
      } else {
         SystemChange( AST__WVTOFR, np, values, args, 1, status );
      }
      break;

/* Wavelength in air to frequency. */
   case AST__AWTOFR:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD && *pv != 0.0 ) {
               *pv = AST__C/( ( *pv )*Refrac( *pv, status ) );
               if( !astISFINITE( *pv ) ) *pv = AST__BAD;
            } else {
               *pv = AST__BAD;
            }
         }
      } else {
         SystemChange( AST__FRTOAW, np, values, args, 1, status );
      }
      break;

/* Frequency to wavelength in air. */
   case AST__FRTOAW:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD && *pv != 0.0 ) {

/* Form the vacuum wavelength. */
               temp = AST__C/( *pv );

/* The refractive index function "Refrac" requires the wavelength in air
   as its parameter. Initially assume that the wavelength in air is equal
   to the vacuum wavelength to get he first estimate of the wavelength in
   air. Then use this estimate to get a better refractive index in order to
   form a better estimate of the air wavelength, etc. Iterate in this way a
   few times. */
               *pv = temp;
               for( iter = 0; iter < 3; iter++ ) {
                  *pv = temp/Refrac( *pv, status );
                  if( !astISFINITE( *pv ) ) {
                     *pv = AST__BAD;
                     break;
                  }
               }

            } else {
               *pv = AST__BAD;
            }
         }
      } else {
         SystemChange( AST__AWTOFR, np, values, args, 1, status );
      }
      break;

/* Radio velocity to relativistic velocity */
   case AST__VRTOVL:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD ) {
               temp = 1.0 - ( *pv )/AST__C;
               temp *= temp;
               *pv = AST__C*( 1.0 - temp )/( 1.0 + temp );
               if( !astISFINITE( *pv ) ) *pv = AST__BAD;
            }
         }
      } else {
         SystemChange( AST__VLTOVR, np, values, args, 1, status );
      }
      break;

/* Relativistic velocity to radio velocity. */
   case AST__VLTOVR:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD ) {
               temp = AST__C + ( *pv );
               if( temp != 0.0 ) {
                  temp = (AST__C - *pv )/temp;
                  if( temp >= 0.0 ) {
                     *pv = AST__C*( 1.0 - sqrt( temp ) );
                     if( !astISFINITE( *pv ) ) *pv = AST__BAD;
                  } else {
                     *pv = AST__BAD;
                  }
               } else {
                  *pv = AST__BAD;
               }
            }
         }
      } else {
         SystemChange( AST__VRTOVL, np, values, args, 1, status );
      }
      break;

/* Optical velocity to relativistic velocity */
   case AST__VOTOVL:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD ) {
               temp = 1.0 + ( *pv )/AST__C;
               temp *= temp;
               *pv = AST__C*( temp - 1.0 )/( temp + 1.0 );
               if( !astISFINITE( *pv ) ) *pv = AST__BAD;
            }
         }
      } else {
         SystemChange( AST__VLTOVO, np, values, args, 1, status );
      }
      break;

/* Relativistic velocity to optical velocity. */
   case AST__VLTOVO:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD ) {
               temp = AST__C - *pv;
               if( temp != 0.0 ) {
                  temp = (AST__C + *pv )/temp;
                  if( temp >= 0.0 ) {
                     *pv = AST__C*( sqrt( temp ) - 1.0 );
                     if( !astISFINITE( *pv ) ) *pv = AST__BAD;
                  } else {
                     *pv = AST__BAD;
                  }
               } else {
                  *pv = AST__BAD;
               }
            }
         }
      } else {
         SystemChange( AST__VOTOVL, np, values, args, 1, status );
      }
      break;

/* Redshift to relativistic velocity */
   case AST__ZOTOVL:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD ) {
               temp = 1.0 + ( *pv );
               temp *= temp;
               *pv = AST__C*( temp - 1.0 )/( temp + 1.0 );
               if( !astISFINITE( *pv ) ) *pv = AST__BAD;
            }
         }
      } else {
         SystemChange( AST__VLTOZO, np, values, args, 1, status );
      }
      break;

/* Relativistic velocity to redshift. */
   case AST__VLTOZO:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD ) {
               temp = AST__C - *pv;
               if( temp != 0.0 ) {
                  temp = (AST__C + *pv )/temp;
                  if( temp >= 0.0 ) {
                     *pv = sqrt( temp ) - 1.0;
                     if( !astISFINITE( *pv ) ) *pv = AST__BAD;
                  } else {
                     *pv = AST__BAD;
                  }
               } else {
                  *pv = AST__BAD;
               }
            }
         }
      } else {
         SystemChange( AST__ZOTOVL, np, values, args, 1, status );
      }
      break;

/* Beta factor to relativistic velocity */
   case AST__BTTOVL:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD ) {
               *pv *= AST__C;
            }
         }
      } else {
         SystemChange( AST__VLTOBT, np, values, args, 1, status );
      }
      break;

/* Relativistic velocity to beta factor. */
   case AST__VLTOBT:
      if( forward ) {
         pv = values - 1;
         for( i = 0; i < np; i++ ) {
            pv++;
            if( *pv != AST__BAD ) {
               *pv /= AST__C;
            }
         }
      } else {
         SystemChange( AST__BTTOVL, np, values, args, 1, status );
      }
      break;

/* If the supplied code does not represent a change of system, clear
   the returned flag. */
   default:
      result = 0;
   }

/* Return the result. */
   return result;
}

static double TopoVel( double ra, double dec, FrameDef *def, int *status ) {
/*
*  Name:
*     TopoVel

*  Purpose:
*     Find the velocity of the observer away from the source.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     double TopoVel( double ra, double dec, FrameDef *def, int *status )

*  Class Membership:
*     SpecMap method.

*  Description:
*     This function finds the component of the velocity of the observer away
*     from a specified source position, at a given epoch, in the frame of
*     rest of the Sun.

*  Parameters:
*     ra
*        The RA (rads, FK5 J2000) of the source.
*     dec
*        The Dec (rads, FK5 J2000) of the source.
*     def
*        Pointer to a FrameDef structure which holds the parameters which
*        define the frame, together with cached intermediate results.
*     status
*        Pointer to the inherited status variable.

*  Returns:
*     The component of the frame's velocity away from the position given by
*     "ra" and "dec", in m/s, measured within the Heliographic frame of
*     rest. Zero is returned if an error has already occurred.

*/

/* Local Variables: */
   double deca;              /* Apparent DEC */
   double raa;               /* Apparent RA */
   double vobs;              /* Velocity of observer relative to earth */
   double vearth;            /* Velocity of earth realtive to sun */

/* Check the global error status. */
   if ( !astOK ) return 0.0;

/* If not already done so, get the parameters defining the transformation
   of mean ra and dec to apparent ra and dec, and store in the supplied frame
   definition structure. */
   if( def->amprms[ 0 ] == AST__BAD ) palMappa( 2000.0, def->epoch,
                                                def->amprms );

/* Convert the source position from mean ra and dec to apparent ra and dec. */
   palMapqkz( ra, dec, def->amprms, &raa, &deca );

/* If not already done so, get the local apparent siderial time (in radians)
   and store in the supplied frame definition structure. */
   if( def->last == AST__BAD ) def->last = palGmst( def->epoch ) +
                                           palEqeqx( def->epoch ) +
                                           def->obslon;

/* Get the component away from the source, of the velocity of the observer
   relative to the centre of the earth (in m/s). */
   vobs = 1000.0*Rverot( def->obslat, def->obsalt, raa, deca, def->last,
                         status );

/* Get the component away from the source, of the velocity of the earth's
   centre relative to the Sun, in m/s. */
   vearth = GeoVel( ra, dec, def, status );

/* Return the total velocity of the observer away from the source in the
   frame of the sun. */
   return vobs + vearth;
}

static AstPointSet *Transform( AstMapping *this, AstPointSet *in,
                               int forward, AstPointSet *out, int *status ) {
/*
*  Name:
*     Transform

*  Purpose:
*     Apply a SpecMap to transform a set of points.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     AstPointSet *Transform( AstMapping *this, AstPointSet *in,
*                             int forward, AstPointSet *out, int *status )

*  Class Membership:
*     SpecMap member function (over-rides the astTransform method inherited
*     from the Mapping class).

*  Description:
*     This function takes a SpecMap and a set of points encapsulated
*     in a PointSet and transforms the points so as to perform the
*     sequence of spectral coordinate conversions specified by
*     previous invocations of astSpecAdd.

*  Parameters:
*     this
*        Pointer to the SpecMap.
*     in
*        Pointer to the PointSet holding the input coordinate data.
*     forward
*        A non-zero value indicates that the forward coordinate transformation
*        should be applied, while a zero value requests the inverse
*        transformation.
*     out
*        Pointer to a PointSet which will hold the transformed (output)
*        coordinate values. A NULL value may also be given, in which case a
*        new PointSet will be created by this function.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     Pointer to the output (possibly new) PointSet.

*  Notes:
*     -  A null pointer will be returned if this function is invoked with the
*     global error status set, or if it should fail for any reason.
*     -  The number of coordinate values per point in the input PointSet must
*     match the number of coordinates for the SpecMap being applied.
*     -  If an output PointSet is supplied, it must have space for sufficient
*     number of points and coordinate values per point to accommodate the
*     result. Any excess space will be ignored.
*/

/* Local Variables: */
   AstPointSet *result;          /* Pointer to output PointSet */
   AstSpecMap *map;              /* Pointer to SpecMap to be applied */
   double **ptr_in;              /* Pointer to input coordinate data */
   double **ptr_out;             /* Pointer to output coordinate data */
   double *spec;                 /* Pointer to output spectral axis value array */
   double *alpha;                /* Pointer to output RA axis value array */
   double *beta;                 /* Pointer to output DEC axis value array */
   int cvt;                      /* Loop counter for conversions */
   int end;                      /* Termination index for conversion loop */
   int inc;                      /* Increment for conversion loop */
   int map3d;                    /* Is the SpecMap 3-dimensional? */
   int ncoord_in;                /* Number of coordinates per input point */
   int npoint;                   /* Number of points */
   int start;                    /* Starting index for conversion loop */

/* Check the global error status. */
   if ( !astOK ) return NULL;

/* Obtain a pointer to the SpecMap. */
   map = (AstSpecMap *) this;

/* Apply the parent mapping using the stored pointer to the Transform member
   function inherited from the parent Mapping class. This function validates
   all arguments and generates an output PointSet if necessary, but does not
   actually transform any coordinate values. */
   result = (*parent_transform)( this, in, forward, out, status );

/* We will now extend the parent astTransform method by performing the
   coordinate conversions needed to generate the output coordinate values. */

/* Determine the numbers of points and coordinates per point from the input
   PointSet and obtain pointers for accessing the input and output coordinate
   values. */
   ncoord_in = astGetNcoord( in );
   npoint = astGetNpoint( in );
   ptr_in = astGetPoints( in );
   ptr_out = astGetPoints( result );

/* Determine whether to apply the forward or inverse transformation, according
   to the direction specified and whether the mapping has been inverted. */
   if ( astGetInvert( this ) ) forward = !forward;

/* Transform the coordinate values. */
/* -------------------------------- */
/* Use "spec" as a synonym for the array of spectral axis values stored in
   the output PointSet. */
   if ( astOK ) {
      spec = ptr_out[ 0 ];

/* If this is a 3D SpecMap use "alpha" as a synonym for the array of RA axis
   values and "beta" as a synonym for the array of DEC axis values stored
   in the output PointSet. */
      map3d = ( ncoord_in == 3 );
      if( map3d ) {
         alpha = ptr_out[ 1 ];
         beta = ptr_out[ 2 ];
      } else {
         alpha = NULL;
         beta = NULL;
      }

/* Initialise the output coordinate values by copying the input ones. */
      (void) memcpy( spec, ptr_in[ 0 ], sizeof( double ) * (size_t) npoint );
      if( map3d ) {
         (void) memcpy( alpha, ptr_in[ 1 ], sizeof( double ) * (size_t) npoint );
         (void) memcpy( beta, ptr_in[ 2 ], sizeof( double ) * (size_t) npoint );
      }

/* We will loop to apply each spectral coordinate conversion in turn to the
   (spec) array. However, if the inverse transformation was requested,
   we must loop through these transformations in reverse order, so set up
   appropriate limits and an increment to control this loop. */
      start = forward ? 0 : map->ncvt - 1;
      end = forward ? map->ncvt : -1;
      inc = forward ? 1 : -1;

/* Loop through the coordinate conversions in the required order. */
      for ( cvt = start; cvt != end; cvt += inc ) {

/* Process conversions which correspond to changes of reference frames. */
         if( !FrameChange( map->cvttype[ cvt ], npoint, alpha, beta, spec,
                          map->cvtargs[ cvt ], forward, status ) ) {

/* If this conversion was not a change of reference frame, it must be a
   change of system. */
            SystemChange( map->cvttype[ cvt ], npoint, spec,
                          map->cvtargs[ cvt ], forward, status );
         }
      }
   }

/* If an error has occurred and a new PointSet may have been created, then
   clean up by annulling it. In any case, ensure that a NULL result is
   returned.*/
   if ( !astOK ) {
      if ( !out ) result = astAnnul( result );
      result = NULL;
   }

/* Return a pointer to the output PointSet. */
   return result;

}

static double UserVel( double ra, double dec, FrameDef *def, int *status ) {
/*
*  Name:
*     UserVel

*  Purpose:
*     Find the component of the velocity of the user-defined rest-frame
*     away from the source.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     double UserVel( double ra, double dec, FrameDef *def, int *status )

*  Class Membership:
*     SpecMap method.

*  Description:
*     This function finds the component of the velocity of the user-defined
*     rest-frame away from a specified position. The magnitude and direction
*     of the rest-frames velocity are defined within the supplied "def"
*     structure. The user-defined rest-frame is typically used to represent
*     the velocity of the source within the heliocentric rest-frame.

*  Parameters:
*     ra
*        The RA (rads, FK5 J2000) of the source.
*     dec
*        The Dec (rads, FK5 J2000) of the source.
*     def
*        Pointer to a FrameDef structure which holds the parameters which
*        define the frame, together with cached intermediate results.
*     status
*        Pointer to the inherited status variable.

*  Returns:
*     The component of the frame's velocity away from the position given by
*     "ra" and "dec", in m/s, measured within the Heliographic frame of
*     rest. Zero is returned if an error has already occurred.

*  Notes:
*     - The direction of the user velocity is given by def->refra and
*     def->refdec (an FK5 J2000 position). The maginitude of the velocity
*     is given by def->veluser, in m/s, positive when the source is moving
*     away from the observer towards def->refra, def->refdec, and given
*     with respect to the heliocentric rest-frame.

*/

/* Local Variables: */
   double vb[ 3 ];          /* Source position vector */

/* Check the global error status. */
   if ( !astOK ) return 0.0;

/* If not already done so, express the user velocity in the form of a
   J2000.0 x,y,z vector. */
   if( def->vuser[ 0 ] == AST__BAD ) {
      def->vuser[ 0 ] = def->veluser*cos( def->refra )*cos( def->refdec );
      def->vuser[ 1 ] = def->veluser*sin( def->refra )*cos( def->refdec );
      def->vuser[ 2 ] = def->veluser*sin( def->refdec );
   }

/* Convert given J2000 RA,Dec to x,y,z. */
   palDcs2c( ra, dec, vb );

/* Return the dot product with the user velocity. Invert it to get the
   velocity towards the observer (the def->veluser value is supposed to be
   positive if the source is moving away from the observer). */
   return -palDvdv( def->vuser, vb );
}

/* Copy constructor. */
/* ----------------- */
static void Copy( const AstObject *objin, AstObject *objout, int *status ) {
/*
*  Name:
*     Copy

*  Purpose:
*     Copy constructor for SpecMap objects.

*  Type:
*     Private function.

*  Synopsis:
*     void Copy( const AstObject *objin, AstObject *objout, int *status )

*  Description:
*     This function implements the copy constructor for SpecMap objects.

*  Parameters:
*     objin
*        Pointer to the object to be copied.
*     objout
*        Pointer to the object being constructed.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     void

*  Notes:
*     -  This constructor makes a deep copy.
*/

/* Local Variables: */
   AstSpecMap *in;                /* Pointer to input SpecMap */
   AstSpecMap *out;               /* Pointer to output SpecMap */
   int cvt;                       /* Loop counter for coordinate conversions */

/* Check the global error status. */
   if ( !astOK ) return;

/* Obtain pointers to the input and output SpecMap structures. */
   in = (AstSpecMap *) objin;
   out = (AstSpecMap *) objout;

/* For safety, first clear any references to the input memory from the output
   SpecMap. */
   out->cvtargs = NULL;
   out->cvttype = NULL;

/* Allocate memory for the output array of argument list pointers. */
   out->cvtargs = astMalloc( sizeof( double * ) * (size_t) in->ncvt );

/* If necessary, allocate memory and make a copy of the input array of
   coordinate conversion codes. */
   if ( in->cvttype ) out->cvttype = astStore( NULL, in->cvttype,
                                               sizeof( int )
                                               * (size_t) in->ncvt );

/* If OK, loop through each conversion in the input SpecMap and make a copy of
   its argument list, storing the new pointer in the output argument list
   array. */
   if ( astOK ) {
      for ( cvt = 0; cvt < in->ncvt; cvt++ ) {
         out->cvtargs[ cvt ] = astStore( NULL, in->cvtargs[ cvt ],
                                         astSizeOf( in->cvtargs[ cvt ] ) );
      }

/* If an error occurred while copying the argument lists, loop through the
   conversions again and clean up by ensuring that the new memory allocated for
   each argument list is freed. */
      if ( !astOK ) {
         for ( cvt = 0; cvt < in->ncvt; cvt++ ) {
            out->cvtargs[ cvt ] = astFree( out->cvtargs[ cvt ] );
	 }
      }
   }

/* If an error occurred, free all other memory allocated above. */
   if ( !astOK ) {
      out->cvtargs = astFree( out->cvtargs );
      out->cvttype = astFree( out->cvttype );
   }
}

/* Destructor. */
/* ----------- */
static void Delete( AstObject *obj, int *status ) {
/*
*  Name:
*     Delete

*  Purpose:
*     Destructor for SpecMap objects.

*  Type:
*     Private function.

*  Synopsis:
*     void Delete( AstObject *obj, int *status )

*  Description:
*     This function implements the destructor for SpecMap objects.

*  Parameters:
*     obj
*        Pointer to the object to be deleted.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     void

*  Notes:
*     This function attempts to execute even if the global error status is
*     set.
*/

/* Local Variables: */
   AstSpecMap *this;              /* Pointer to SpecMap */
   int cvt;                       /* Loop counter for coordinate conversions */

/* Obtain a pointer to the SpecMap structure. */
   this = (AstSpecMap *) obj;

/* Loop to free the memory containing the argument list for each coordinate
   conversion. */
   for ( cvt = 0; cvt < this->ncvt; cvt++ ) {
      this->cvtargs[ cvt ] = astFree( this->cvtargs[ cvt ] );
   }

/* Free the memory holding the array of conversion types and the array of
   argument list pointers. */
   this->cvtargs = astFree( this->cvtargs );
   this->cvttype = astFree( this->cvttype );
}

/* Dump function. */
/* -------------- */
static void Dump( AstObject *this_object, AstChannel *channel, int *status ) {
/*
*  Name:
*     Dump

*  Purpose:
*     Dump function for SpecMap objects.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     void Dump( AstObject *this, AstChannel *channel, int *status )

*  Description:
*     This function implements the Dump function which writes out data
*     for the SpecMap class to an output Channel.

*  Parameters:
*     this
*        Pointer to the SpecMap whose data are being written.
*     channel
*        Pointer to the Channel to which the data are being written.
*     status
*        Pointer to the inherited status variable.
*/

/* Local Constants: */
#define KEY_LEN 50               /* Maximum length of a keyword */

/* Local Variables: */
   AstSpecMap *this;             /* Pointer to the SpecMap structure */
   char key[ KEY_LEN + 1 ];      /* Buffer for keyword string */
   const char *argdesc[ MAX_ARGS ]; /* Pointers to argument descriptions */
   const char *comment;          /* Pointer to comment string */
   const char *sval;             /* Pointer to string value */
   int argdec;                   /* Index of DEC argument */
   int argra;                    /* Index of RA argument */
   int iarg;                     /* Loop counter for arguments */
   int icvt;                     /* Loop counter for conversion steps */
   int ival;                     /* Integer value */
   int nargs;                    /* Number of user-supplied arguments */
   int szargs;                   /* Number of stored arguments */
   int set;                      /* Attribute value set? */

/* Check the global error status. */
   if ( !astOK ) return;

/* Obtain a pointer to the SpecMap structure. */
   this = (AstSpecMap *) this_object;

/* Write out values representing the instance variables for the SpecMap
   class.  Accompany these with appropriate comment strings, possibly
   depending on the values being written.*/

/* In the case of attributes, we first use the appropriate (private)
   Test...  member function to see if they are set. If so, we then use
   the (private) Get... function to obtain the value to be written
   out.

   For attributes which are not set, we use the astGet... method to
   obtain the value instead. This will supply a default value
   (possibly provided by a derived class which over-rides this method)
   which is more useful to a human reader as it corresponds to the
   actual default attribute value.  Since "set" will be zero, these
   values are for information only and will not be read back. */

/* Number of conversion steps. */
/* --------------------------- */
/* Regard this as "set" if it is non-zero. */
   ival = this->ncvt;
   set = ( ival != 0 );
   astWriteInt( channel, "Nspec", set, 0, ival, "Number of conversion steps" );

/* Write out data for each conversion step... */
   for ( icvt = 0; icvt < this->ncvt; icvt++ ) {

/* Conversion type. */
/* ---------------- */
/* Change each conversion type code into an equivalent string and
   obtain associated descriptive information. If the conversion code
   was not recognised, report an error and give up. */
      if ( astOK ) {
         sval = CvtString( this->cvttype[ icvt ], &comment, &argra, &argdec,
                           &nargs, &szargs, argdesc, status );
         if ( astOK && !sval ) {
            astError( AST__SPCIN,
                      "astWrite(%s): Corrupt %s contains invalid SpecMap "
                      "spectral coordinate conversion code (%d).", status,
                      astGetClass( channel ), astGetClass( this ),
                      (int) this->cvttype[ icvt ] );
            break;
         }

/* Create an appropriate keyword and write out the conversion code
   information. */
         (void) sprintf( key, "Spec%d", icvt + 1 );
         astWriteString( channel, key, 1, 1, sval, comment );

/* Write out data for each conversion argument... */
         for ( iarg = 0; iarg < szargs; iarg++ ) {

/* Arguments. */
/* ---------- */
/* Create an appropriate keyword and write out the argument value,
   accompanied by the descriptive comment obtained above. */
            if( this->cvtargs[ icvt ][ iarg ] != AST__BAD ) {
               (void) sprintf( key, "Spec%d%c", icvt + 1, ALPHABET[ iarg ] );
               astWriteDouble( channel, key, 1, 1, this->cvtargs[ icvt ][ iarg ],
                               argdesc[ iarg ] );
            }
         }

/* Quit looping if an error occurs. */
         if ( !astOK ) break;
      }
   }

/* Undefine macros local to this function. */
#undef KEY_LEN
}

/* Standard class functions. */
/* ========================= */
/* Implement the astIsASpecMap and astCheckSpecMap functions using the macros
   defined for this purpose in the "object.h" header file. */
astMAKE_ISA(SpecMap,Mapping)
astMAKE_CHECK(SpecMap)

AstSpecMap *astSpecMap_( int nin, int flags, const char *options, int *status, ...) {
/*
*++
*  Name:
c     astSpecMap
f     AST_SPECMAP

*  Purpose:
*     Create a SpecMap.

*  Type:
*     Public function.

*  Synopsis:
c     #include "specmap.h"
c     AstSpecMap *astSpecMap( int nin, int flags, const char *options, ... )
f     RESULT = AST_SPECMAP( NIN, FLAGS, OPTIONS, STATUS )

*  Class Membership:
*     SpecMap constructor.

*  Description:
*     This function creates a new SpecMap and optionally initialises
*     its attributes.
*
*     An SpecMap is a specialised form of Mapping which can be used to
*     represent a sequence of conversions between standard spectral
*     coordinate systems. This includes conversions between frequency,
*     wavelength, and various forms of velocity, as well as conversions
*     between different standards of rest.
*
*     When a SpecMap is first created, it simply performs a unit
c     (null) Mapping. Using the astSpecAdd function,
f     (null) Mapping. Using the AST_SPECADD routine,
*     a series of coordinate conversion steps may then be added, selected
*     from the list of supported conversions. This allows multi-step
*     conversions between a variety of spectral coordinate systems to
*     be assembled out of the building blocks provided by this class.
*
*     For details of the individual coordinate conversions available,
c     see the description of the astSpecAdd function.
f     see the description of the AST_SPECADD routine.
*
*     Conversions are available to transform between standards of rest.
*     Such conversions need to know the source position as an RA and DEC.
*     This information can be supplied in the form of parameters for
*     the relevant conversions, in which case the SpecMap is 1-dimensional,
*     simply transforming the spectral axis values. This means that the
*     same source position will always be used by the SpecMap. However, this
*     may not be appropriate for an accurate description of a 3-D spectral
*     cube, where changes of spatial position can produce significant
*     changes in the Doppler shift introduced when transforming between
*     standards of rest. For this situation, a 3-dimensional SpecMap can
*     be created in which axes 2 and 3 correspond to the source RA and DEC
*     The SpecMap simply copies values for axes 2 and 3 from input to
*     output).

*  Parameters:
c     nin
f     NIN = INTEGER (Given)
*        The number of inputs to the Mapping (this will also equal the
*        number of outputs). This value must be either 1 or 3. In either
*        case, the first input and output correspoindis the spectral axis.
*        For a 3-axis SpecMap, the second and third axes give the RA and
*        DEC (J2000 FK5) of the source. This positional information is
*        used by conversions which transform between standards of rest,
*        and replaces the "RA" and "DEC" arguments for the individual
*        conversions listed in description of the "SpecAdd"
c        function.
f        routine.
c     flags
f     FLAGS = INTEGER (Given)
c        This parameter is reserved for future use and should currently
f        This argument is reserved for future use and should currently
*        always be set to zero.
c     options
f     OPTIONS = CHARACTER * ( * ) (Given)
c        Pointer to a null-terminated string containing an optional
c        comma-separated list of attribute assignments to be used for
c        initialising the new SpecMap. The syntax used is identical to
c        that for the astSet function and may include "printf" format
c        specifiers identified by "%" symbols in the normal way.
c        If no initialisation is required, a zero-length string may be
c        supplied.
f        A character string containing an optional comma-separated
f        list of attribute assignments to be used for initialising the
f        new SpecMap. The syntax used is identical to that for the
f        AST_SET routine. If no initialisation is required, a blank
f        value may be supplied.
c     ...
c        If the "options" string contains "%" format specifiers, then
c        an optional list of additional arguments may follow it in
c        order to supply values to be substituted for these
c        specifiers. The rules for supplying these are identical to
c        those for the astSet function (and for the C "printf"
c        function).
f     STATUS = INTEGER (Given and Returned)
f        The global status.

*  Returned Value:
c     astSpecMap()
f     AST_SPECMAP = INTEGER
*        A pointer to the new SpecMap.

*  Notes:
*     - The nature and units of the coordinate values supplied for the
*     first input (i.e. the spectral input) of a SpecMap must be appropriate
*     to the first conversion step applied by the SpecMap. For instance, if
*     the first conversion step is "FRTOVL" (frequency to relativistic
*     velocity), then the coordinate values for the first input should
*     be frequency in units of Hz. Similarly, the nature and units of the
*     coordinate values returned by a SpecMap will be determined by the
*     last conversion step applied by the SpecMap. For instance, if the
*     last conversion step is "VLTOVO" (relativistic velocity to optical
*     velocity), then the coordinate values for the first output will be optical
*     velocity in units of metres per second. See the description of the
c     astSpecAdd function for the units expected and returned by each
f     AST_SPECADD routine for the units expected and returned by each
*     conversion.
*     - A null Object pointer (AST__NULL) will be returned if this
c     function is invoked with the AST error status set, or if it
f     function is invoked with STATUS set to an error value, or if it
*     should fail for any reason.
*--
*/

/* Local Variables: */
   astDECLARE_GLOBALS            /* Pointer to thread-specific global data */
   AstSpecMap *new;              /* Pointer to the new SpecMap */
   va_list args;                 /* Variable argument list */

/* Get a pointer to the thread specific global data structure. */
   astGET_GLOBALS(NULL);

/* Check the global status. */
   if ( !astOK ) return NULL;

/* Initialise the SpecMap, allocating memory and initialising the virtual
   function table as well if necessary. */
   new = astInitSpecMap( NULL, sizeof( AstSpecMap ), !class_init, &class_vtab,
                        "SpecMap", nin, flags );

/* If successful, note that the virtual function table has been initialised. */
   if ( astOK ) {
      class_init = 1;

/* Obtain the variable argument list and pass it along with the options string
   to the astVSet method to initialise the new SpecMap's attributes. */
      va_start( args, status );
      astVSet( new, options, NULL, args );
      va_end( args );

/* If an error occurred, clean up by deleting the new object. */
      if ( !astOK ) new = astDelete( new );
   }

/* Return a pointer to the new SpecMap. */
   return new;
}

AstSpecMap *astSpecMapId_( int nin, int flags, const char *options, ... ) {
/*
*  Name:
*     astSpecMapId_

*  Purpose:
*     Create a SpecMap.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specmap.h"
*     AstSpecMap *astSpecMapId_( int nin, int flags, const char *options, ... )

*  Class Membership:
*     SpecMap constructor.

*  Description:
*     This function implements the external (public) interface to the
*     astSpecMap constructor function. It returns an ID value (instead
*     of a true C pointer) to external users, and must be provided
*     because astSpecMap_ has a variable argument list which cannot be
*     encapsulated in a macro (where this conversion would otherwise
*     occur).
*
*     The variable argument list also prevents this function from
*     invoking astSpecMap_ directly, so it must be a re-implementation
*     of it in all respects, except for the final conversion of the
*     result to an ID value.

*  Parameters:
*     As for astSpecMap_.

*  Returned Value:
*     The ID value associated with the new SpecMap.
*/

/* Local Variables: */
   astDECLARE_GLOBALS            /* Pointer to thread-specific global data */
   AstSpecMap *new;              /* Pointer to the new SpecMap */
   va_list args;                 /* Variable argument list */

   int *status;                  /* Pointer to inherited status value */

/* Get a pointer to the inherited status value. */
   status = astGetStatusPtr;

/* Get a pointer to the thread specific global data structure. */
   astGET_GLOBALS(NULL);

/* Check the global status. */
   if ( !astOK ) return NULL;

/* Initialise the SpecMap, allocating memory and initialising the virtual
   function table as well if necessary. */
   new = astInitSpecMap( NULL, sizeof( AstSpecMap ), !class_init, &class_vtab,
                        "SpecMap", nin, flags );

/* If successful, note that the virtual function table has been initialised. */
   if ( astOK ) {
      class_init = 1;

/* Obtain the variable argument list and pass it along with the options string
   to the astVSet method to initialise the new SpecMap's attributes. */
      va_start( args, options );
      astVSet( new, options, NULL, args );
      va_end( args );

/* If an error occurred, clean up by deleting the new object. */
      if ( !astOK ) new = astDelete( new );
   }

/* Return an ID value for the new SpecMap. */
   return astMakeId( new );
}

AstSpecMap *astInitSpecMap_( void *mem, size_t size, int init,
                             AstSpecMapVtab *vtab, const char *name,
                             int nin, int flags, int *status ) {
/*
*+
*  Name:
*     astInitSpecMap

*  Purpose:
*     Initialise a SpecMap.

*  Type:
*     Protected function.

*  Synopsis:
*     #include "specmap.h"
*     AstSpecMap *astInitSpecMap( void *mem, size_t size, int init,
*                               AstSpecMapVtab *vtab, const char *name,
*                               int nin, int flags )

*  Class Membership:
*     SpecMap initialiser.

*  Description:
*     This function is provided for use by class implementations to initialise
*     a new SpecMap object. It allocates memory (if necessary) to accommodate
*     the SpecMap plus any additional data associated with the derived class.
*     It then initialises a SpecMap structure at the start of this memory. If
*     the "init" flag is set, it also initialises the contents of a virtual
*     function table for a SpecMap at the start of the memory passed via the
*     "vtab" parameter.

*  Parameters:
*     mem
*        A pointer to the memory in which the SpecMap is to be initialised.
*        This must be of sufficient size to accommodate the SpecMap data
*        (sizeof(SpecMap)) plus any data used by the derived class. If a value
*        of NULL is given, this function will allocate the memory itself using
*        the "size" parameter to determine its size.
*     size
*        The amount of memory used by the SpecMap (plus derived class data).
*        This will be used to allocate memory if a value of NULL is given for
*        the "mem" parameter. This value is also stored in the SpecMap
*        structure, so a valid value must be supplied even if not required for
*        allocating memory.
*     init
*        A logical flag indicating if the SpecMap's virtual function table is
*        to be initialised. If this value is non-zero, the virtual function
*        table will be initialised by this function.
*     vtab
*        Pointer to the start of the virtual function table to be associated
*        with the new SpecMap.
*     name
*        Pointer to a constant null-terminated character string which contains
*        the name of the class to which the new object belongs (it is this
*        pointer value that will subsequently be returned by the astClass
*        method).
*     nin
*        The number of inputs and outputs for the SpecMap (either 1 or 3).
*     flags
*        This parameter is reserved for future use. It is currently ignored.

*  Returned Value:
*     A pointer to the new SpecMap.

*  Notes:
*     -  A null pointer will be returned if this function is invoked with the
*     global error status set, or if it should fail for any reason.
*-
*/

/* Local Variables: */
   AstSpecMap *new;               /* Pointer to the new SpecMap */

/* Check the global status. */
   if ( !astOK ) return NULL;

/* Check nin is OK (1 or 3). */
   if( nin != 1 && nin != 3 ) {
      astError( AST__BADNI, "astInitSpecMap(SpecMap): Supplied number of "
                "SpecMap axes (%d) is illegal; it should be 1 or 2. ", status,
                nin );
   }

/* If necessary, initialise the virtual function table. */
   if ( init ) astInitSpecMapVtab( vtab, name );

/* Initialise a 1D Mapping structure (the parent class) as the first component
   within the SpecMap structure, allocating memory if necessary. Specify that
   the Mapping should be defined in both the forward and inverse directions. */
   new = (AstSpecMap *) astInitMapping( mem, size, 0,
                                       (AstMappingVtab *) vtab, name,
                                       nin, nin, 1, 1 );

   if ( astOK ) {

/* Initialise the SpecMap data. */
/* --------------------------- */
/* The initial state is with no conversions set, in which condition the
   SpecMap simply implements a unit mapping. */
      new->ncvt = 0;
      new->cvtargs = NULL;
      new->cvttype = NULL;

/* If an error occurred, clean up by deleting the new object. */
      if ( !astOK ) new = astDelete( new );
   }

/* Return a pointer to the new object. */
   return new;
}

AstSpecMap *astLoadSpecMap_( void *mem, size_t size,
                           AstSpecMapVtab *vtab, const char *name,
                           AstChannel *channel, int *status ) {
/*
*+
*  Name:
*     astLoadSpecMap

*  Purpose:
*     Load a SpecMap.

*  Type:
*     Protected function.

*  Synopsis:
*     #include "specmap.h"
*     AstSpecMap *astLoadSpecMap( void *mem, size_t size,
*                               AstSpecMapVtab *vtab, const char *name,
*                               AstChannel *channel )

*  Class Membership:
*     SpecMap loader.

*  Description:
*     This function is provided to load a new SpecMap using data read
*     from a Channel. It first loads the data used by the parent class
*     (which allocates memory if necessary) and then initialises a
*     SpecMap structure in this memory, using data read from the input
*     Channel.
*
*     If the "init" flag is set, it also initialises the contents of a
*     virtual function table for a SpecMap at the start of the memory
*     passed via the "vtab" parameter.


*  Parameters:
*     mem
*        A pointer to the memory into which the SpecMap is to be
*        loaded.  This must be of sufficient size to accommodate the
*        SpecMap data (sizeof(SpecMap)) plus any data used by derived
*        classes. If a value of NULL is given, this function will
*        allocate the memory itself using the "size" parameter to
*        determine its size.
*     size
*        The amount of memory used by the SpecMap (plus derived class
*        data).  This will be used to allocate memory if a value of
*        NULL is given for the "mem" parameter. This value is also
*        stored in the SpecMap structure, so a valid value must be
*        supplied even if not required for allocating memory.
*
*        If the "vtab" parameter is NULL, the "size" value is ignored
*        and sizeof(AstSpecMap) is used instead.
*     vtab
*        Pointer to the start of the virtual function table to be
*        associated with the new SpecMap. If this is NULL, a pointer to
*        the (static) virtual function table for the SpecMap class is
*        used instead.
*     name
*        Pointer to a constant null-terminated character string which
*        contains the name of the class to which the new object
*        belongs (it is this pointer value that will subsequently be
*        returned by the astGetClass method).
*
*        If the "vtab" parameter is NULL, the "name" value is ignored
*        and a pointer to the string "SpecMap" is used instead.

*  Returned Value:
*     A pointer to the new SpecMap.

*  Notes:
*     - A null pointer will be returned if this function is invoked
*     with the global error status set, or if it should fail for any
*     reason.
*-
*/

/* Local Constants: */
   astDECLARE_GLOBALS            /* Pointer to thread-specific global data */
#define KEY_LEN 50               /* Maximum length of a keyword */

/* Local Variables: */
   AstSpecMap *new;              /* Pointer to the new SpecMap */
   char *sval;                   /* Pointer to string value */
   char key[ KEY_LEN + 1 ];      /* Buffer for keyword string */
   const char *argdesc[ MAX_ARGS ]; /* Pointers to argument descriptions */
   const char *comment;          /* Pointer to comment string */
   int argdec;                   /* Index of DEC argument */
   int argra;                    /* Index of RA argument */
   int iarg;                     /* Loop counter for arguments */
   int icvt;                     /* Loop counter for conversion steps */
   int nargs;                    /* Number of user-supplied arguments */
   int szargs;                   /* Number of stored arguments */

/* Get a pointer to the thread specific global data structure. */
   astGET_GLOBALS(channel);

/* Initialise. */
   new = NULL;

/* Check the global error status. */
   if ( !astOK ) return new;

/* If a NULL virtual function table has been supplied, then this is
   the first loader to be invoked for this SpecMap. In this case the
   SpecMap belongs to this class, so supply appropriate values to be
   passed to the parent class loader (and its parent, etc.). */
   if ( !vtab ) {
      size = sizeof( AstSpecMap );
      vtab = &class_vtab;
      name = "SpecMap";

/* If required, initialise the virtual function table for this class. */
      if ( !class_init ) {
         astInitSpecMapVtab( vtab, name );
         class_init = 1;
      }
   }

/* Invoke the parent class loader to load data for all the ancestral
   classes of the current one, returning a pointer to the resulting
   partly-built SpecMap. */
   new = astLoadMapping( mem, size, (AstMappingVtab *) vtab, name,
                         channel );

   if ( astOK ) {

/* Read input data. */
/* ================ */
/* Request the input Channel to read all the input data appropriate to
   this class into the internal "values list". */
      astReadClassData( channel, "SpecMap" );

/* Now read each individual data item from this list and use it to
   initialise the appropriate instance variable(s) for this class. */

/* In the case of attributes, we first read the "raw" input value,
   supplying the "unset" value as the default. If a "set" value is
   obtained, we then use the appropriate (private) Set... member
   function to validate and set the value properly. */

/* Number of conversion steps. */
/* --------------------------- */
/* Read the number of conversion steps and allocate memory to hold
   data for each step. */
      new->ncvt = astReadInt( channel, "nspec", 0 );
      if ( new->ncvt < 0 ) new->ncvt = 0;
      new->cvttype = astMalloc( sizeof( int ) * (size_t) new->ncvt );
      new->cvtargs = astMalloc( sizeof( double * ) * (size_t) new->ncvt );

/* If an error occurred, ensure that all allocated memory is freed. */
      if ( !astOK ) {
         new->cvttype = astFree( new->cvttype );
         new->cvtargs = astFree( new->cvtargs );

/* Otherwise, initialise the argument pointer array. */
      } else {
         for ( icvt = 0; icvt < new->ncvt; icvt++ ) {
            new->cvtargs[ icvt ] = NULL;
         }

/* Read in data for each conversion step... */
         for ( icvt = 0; icvt < new->ncvt; icvt++ ) {

/* Conversion type. */
/* ---------------- */
/* Create an appropriate keyword and read the string representation of
   the conversion type. */
            (void) sprintf( key, "spec%d", icvt + 1 );
            sval = astReadString( channel, key, NULL );

/* If no value was read, report an error. */
            if ( astOK ) {
               if ( !sval ) {
                  astError( AST__BADIN,
                            "astRead(%s): A spectral coordinate conversion "
                            "type is missing from the input SpecMap data.", status,
                            astGetClass( channel ) );

/* Otherwise, convert the string representation into the required
   conversion type code. */
               } else {
                  new->cvttype[ icvt ] = CvtCode( sval, status );

/* If the string was not recognised, report an error. */
                  if ( new->cvttype[ icvt ] == AST__SPEC_NULL ) {
                     astError( AST__BADIN,
                              "astRead(%s): Invalid spectral conversion "
                              "type \"%s\" in SpecMap data.", status,
                              astGetClass( channel ), sval );
                  }
               }

/* Free the memory holding the string value. */
               sval = astFree( sval );
            }

/* Obtain the number of arguments associated with the conversion and
   allocate memory to hold them. */
            (void) CvtString( new->cvttype[ icvt ], &comment, &argra,
                              &argdec, &nargs, &szargs, argdesc, status );
            new->cvtargs[ icvt ] = astMalloc( sizeof( double ) *
                                              (size_t) szargs );

/* Read in data for each argument... */
            if ( astOK ) {
               for ( iarg = 0; iarg < szargs; iarg++ ) {

/* Arguments. */
/* ---------- */
/* Create an appropriate keyword and read each argument value. */
                  (void) sprintf( key, "spec%d%c", icvt + 1, ALPHABET[ iarg ] );
                  new->cvtargs[ icvt ][ iarg ] = astReadDouble( channel, key,
                                                                AST__BAD );
               }
            }

/* Quit looping if an error occurs. */
            if ( !astOK ) break;
         }
      }

/* If an error occurred, clean up by deleting the new SpecMap. */
      if ( !astOK ) new = astDelete( new );
   }

/* Return the new SpecMap pointer. */
   return new;

/* Undefine macros local to this function. */
#undef KEY_LEN
}

/* Virtual function interfaces. */
/* ============================ */
/* These provide the external interface to the virtual functions defined by
   this class. Each simply checks the global error status and then locates and
   executes the appropriate member function, using the function pointer stored
   in the object's virtual function table (this pointer is located using the
   astMEMBER macro defined in "object.h").

   Note that the member function may not be the one defined here, as it may
   have been over-ridden by a derived class. However, it should still have the
   same interface. */
void astSpecAdd_( AstSpecMap *this, const char *cvt, int narg,
                  const double args[], int *status ) {
   if ( !astOK ) return;
   (**astMEMBER(this,SpecMap,SpecAdd))( this, cvt, narg, args, status );
}