upgrade ast 8.7.1

1 files changed, 4448 insertions, 0 deletions

diff --git a/ast/prism.c b/ast/prism.c
new file mode 100644
index 0000000..38281f3
--- /dev/null
+++ b/ast/prism.c
@@ -0,0 +1,4448 @@
+/*
+*class++
+*  Name:
+*     Prism
+
+*  Purpose:
+*     An extrusion of a region into higher dimensions.
+
+*  Constructor Function:
+c     astPrism
+f     AST_PRISM
+
+*  Description:
+*     A Prism is a Region which represents an extrusion of an existing Region
+*     into one or more orthogonal dimensions (specified by another Region).
+*     If the Region to be extruded has N axes, and the Region defining the
+*     extrusion has M axes, then the resulting Prism will have (M+N) axes.
+*     A point is inside the Prism if the first N axis values correspond to
+*     a point inside the Region being extruded, and the remaining M axis
+*     values correspond to a point inside the Region defining the extrusion.
+*
+*     As an example, a cylinder can be represented by extruding an existing
+*     Circle, using an Interval to define the extrusion. Ih this case, the
+*     Interval would have a single axis and would specify the upper and
+*     lower limits of the cylinder along its length.
+
+*  Inheritance:
+*     The Prism class inherits from the Region class.
+
+*  Attributes:
+*     The Prism class does not define any new attributes beyond those
+*     which are applicable to all Regions.
+
+*  Functions:
+c     The Prism class does not define any new functions beyond those
+f     The Prism class does not define any new routines beyond those
+*     which are applicable to all Regions.
+
+*  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:
+*     17-DEC-2004 (DSB):
+*        Original version.
+*     11-MAY-2005 (DSB):
+*        Overlap modified to allow testing of overlap between prisms and
+*        intervals.
+*     14-FEB-2006 (DSB):
+*        Override astGetObjSize.
+*     9-OCT-2007 (DSB):
+*        Guard against all axes being extrusion axes in EquivPrism.
+*     20-JAN-2009 (DSB):
+*        Over-ride astRegBasePick.
+*     22-JAN-2009 (DSB):
+*        - Allow any class of Region to be used to define the extrusion axes.
+*        - Over-ride the astMapList method.
+*     19-MAR-2009 (DSB):
+*        Over-ride the astDecompose method.
+*     14-AUG-2014 (DSB):
+*        Over-ride the astGetRegionBounds method.
+*     9-SEP-2014 (DSB):
+*        Record the pointer to the Prism implementation of RegBaseMesh
+*        within the class virtual function table.
+*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 Prism
+
+/* Include files. */
+/* ============== */
+/* Interface definitions. */
+/* ---------------------- */
+
+#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 "region.h"              /* Regions (parent class) */
+#include "channel.h"             /* I/O channels */
+#include "prism.h"               /* Interface definition for this class */
+#include "cmpmap.h"              /* Compound Mappings */
+#include "cmpframe.h"            /* Compound Frames */
+#include "unitmap.h"             /* Unit Mappings */
+#include "interval.h"            /* Axis intervals */
+#include "pointlist.h"           /* Points within Frames */
+#include "permmap.h"             /* Axis permutations */
+
+/* Error code definitions. */
+/* ----------------------- */
+#include "ast_err.h"             /* AST error codes */
+
+/* C header files. */
+/* --------------- */
+#include <stdarg.h>
+#include <stddef.h>
+#include <string.h>
+#include <stdio.h>
+#include <math.h>
+#include <limits.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 AstMapping *(* parent_simplify)( AstMapping *, int * );
+static AstPointSet *(* parent_transform)( AstMapping *, AstPointSet *, int, AstPointSet *, int * );
+static AstRegion *(* parent_getdefunc)( AstRegion *, int * );
+static double (*parent_getfillfactor)( AstRegion *, int * );
+static int (* parent_equal)( AstObject *, AstObject *, int * );
+static int (* parent_getobjsize)( AstObject *, int * );
+static int (* parent_maplist)( AstMapping *, int, int, int *, AstMapping ***, int **, int * );
+static int (* parent_overlapx)( AstRegion *, AstRegion *, int * );
+static void (* parent_clearclosed)( AstRegion *, int * );
+static void (* parent_clearmeshsize)( AstRegion *, int * );
+static void (* parent_setclosed)( AstRegion *, int, int * );
+static void (* parent_setmeshsize)( AstRegion *, int, int * );
+static void (* parent_setregfs)( AstRegion *, AstFrame *, int * );
+static void (*parent_getregionbounds)( AstRegion *, double *, double *, int * );
+static void (*parent_regclearattrib)( AstRegion *, const char *, char **, int * );
+static void (*parent_regsetattrib)( AstRegion *, const char *, char **, int * );
+
+#if defined(THREAD_SAFE)
+static int (* parent_managelock)( AstObject *, int, int, AstObject **, int * );
+#endif
+
+
+#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(Prism)
+
+/* Define macros for accessing each item of thread specific global data. */
+#define class_init astGLOBAL(Prism,Class_Init)
+#define class_vtab astGLOBAL(Prism,Class_Vtab)
+
+
+#include <pthread.h>
+
+
+#else
+
+
+/* Define the class virtual function table and its initialisation flag
+   as static variables. */
+static AstPrismVtab class_vtab;   /* Virtual function table */
+static int class_init = 0;       /* Virtual function table initialised? */
+
+#endif
+
+/* 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. */
+AstPrism *astPrismId_( void *, void *, const char *, ... );
+
+/* Prototypes for Private Member Functions. */
+/* ======================================== */
+static AstMapping *Simplify( AstMapping *, int * );
+static AstPointSet *RegBaseMesh( AstRegion *, int * );
+static AstPointSet *Transform( AstMapping *, AstPointSet *, int, AstPointSet *, int * );
+static AstRegion *GetDefUnc( AstRegion *, int * );
+static AstRegion *RegBasePick( AstRegion *this, int, const int *, int * );
+static double *RegCentre( AstRegion *this, double *, double **, int, int, int * );
+static double GetFillFactor( AstRegion *, int * );
+static int Equal( AstObject *, AstObject *, int * );
+static int GetBounded( AstRegion *, int * );
+static int GetObjSize( AstObject *, int * );
+static int MapList( AstMapping *, int, int, int *, AstMapping ***, int **, int * );
+static int Overlap( AstRegion *, AstRegion *, int * );
+static int OverlapX( AstRegion *, AstRegion *, int * );
+static int RegPins( AstRegion *, AstPointSet *, AstRegion *, int **, int * );
+static void ClearClosed( AstRegion *, int * );
+static void ClearMeshSize( AstRegion *, int * );
+static void Copy( const AstObject *, AstObject *, int * );
+static void Decompose( AstMapping *, AstMapping **, AstMapping **, int *, int *, int *, int * );
+static void Delete( AstObject *, int * );
+static void Dump( AstObject *, AstChannel *, int * );
+static void GetRegions( AstPrism *, AstRegion **, AstRegion **, int *, int * );
+static void GetRegionBounds( AstRegion *, double *, double *, int * );
+static void RegBaseBox( AstRegion *, double *, double *, int * );
+static void RegClearAttrib( AstRegion *, const char *, char **, int * );
+static void RegSetAttrib( AstRegion *, const char *, char **, int * );
+static void SetClosed( AstRegion *, int, int * );
+static void SetMeshSize( AstRegion *, int, int * );
+static void SetRegFS( AstRegion *, AstFrame *, int * );
+
+#if defined(THREAD_SAFE)
+static int ManageLock( AstObject *, int, int, AstObject **, int * );
+#endif
+
+
+/* Member functions. */
+/* ================= */
+AstRegion *astConvertToPrism_( AstRegion *this, int *status ) {
+/*
+*+
+*  Name:
+*     astConvertToPrism
+
+*  Purpose:
+*     Convert a supplied Region into a Prism if possible.
+
+*  Type:
+*     Protected function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     AstRegion *astConvertToPrism( AstRegion *this, int *status )
+
+*  Description:
+*     This function attempts to split the supplied Region into two
+*     regions defined within separate coordinate system. If this is
+*     possible, and if either one of the two resulting Regions can be
+*     simplified, then the two simplified Regions are joined into a Prism
+*     equivalent to the supplied Region. The Prism is then simplified and
+*     returned.
+*
+*     If the supplied Region cannot be split into two components, or if
+*     neither of the two components can eb simplified, then a clone of the
+*     supplied Region pointer is returned.
+
+*  Parameters:
+*     this
+*        Pointer to the original Region.
+*     status
+*        Pointer to the inherited status variable.
+
+*  Returned Value:
+*     A pointer to the equivalent simplified Prism, or a clone of the
+*     supplied Region pointer.
+
+*  Notes:
+*     - A NULL pointer value will be returned if this function is
+*     invoked with the AST error status set, or if it should fail for
+*     any reason.
+*-
+*/
+
+/* Local Variables: */
+   AstFrame *frm;                /* Current Frame in supplied Region */
+   AstFrame *pickfrm1;           /* Frame formed by picking current subset of axes */
+   AstFrame *pickfrm2;           /* Frame formed by picking all other axes */
+   AstMapping *junk;             /* Unused Mapping pointer */
+   AstMapping *map;              /* Base -> current Mapping */
+   AstPrism *prism;              /* Prism combining all axes */
+   AstPrism *newprism;           /* Prism combining all axes, in original Frame */
+   AstRegion *result;            /* Result pointer to return */
+   AstRegion *sp1;               /* Simplified region spanning selected axes */
+   AstRegion *sp2;               /* Simplified region spanning unselected axes */
+   AstUnitMap *um;               /* A UnitMap */
+   int *ax;                      /* Pointer to array of selecte axis indices */
+   int *perm;                    /* Axis permutation array */
+   int axis;                     /* Axis index */
+   int bitmask;                  /* Integer with set bits for selected axes */
+   int i;                        /* Loop index */
+   int mask;                     /* Integer with a set bit at current axis */
+   int nax;                      /* Number of selected axes */
+   int nin;                      /* No. of base Frame axes (Mapping inputs) */
+   int nout;                     /* No. of current Frame axes (Mapping outputs) */
+   int topmask;                  /* Integer that selects all axes */
+
+/* Initialise. */
+   result = NULL;
+
+/* Check the global error status. */
+   if ( !astOK ) return result;
+
+/* Get the Mapping from base to current Frame. */
+   map = astGetMapping( this->frameset, AST__BASE, AST__CURRENT );
+
+/* Get the number of inputs and outputs for the Mapping. */
+   nin = astGetNin( map );
+   nout = astGetNout( map );
+
+/* Allocate memory to hold the indices of the current Frame axes in the
+   current subset */
+   ax = astMalloc( sizeof( int )* nout );
+   if( ax ) {
+
+/* We need to scan through all possible subsets of the current Frame
+   axes, looking for a subset that results in the Region being split.
+   We use the binary pattern of bits in "bitmask" to indicate if the
+   corresponding axes should be included in the subset of axes.
+   Loop round all possible combinations, until a combination is found
+   that results in a Prism being formed. */
+      topmask = pow( 2, nout );
+      for( bitmask = 1; bitmask < topmask  && !result; bitmask++ ) {
+
+/* Store the indices of the axes forming the current subset. */
+         nax = 0;
+         mask = 1;
+         for( axis = 0; axis < nout; axis++  ) {
+            if( bitmask & mask ) ax[ nax++ ] = axis;
+            mask <<= 1;
+         }
+
+/* See if the current subset of current Frame axes can be split off from
+   the Region. If it can, the Frame pointer returned by astPickAxes will identify
+   a Region. */
+         pickfrm1 = astPickAxes( this, nax, ax, &junk );
+         junk = astAnnul( junk );
+         if( astIsARegion( pickfrm1 ) ) {
+
+/* Check that the remaining (unselected) axes can also be picked into a
+   new Region. */
+            nax = 0;
+            mask = 1;
+            for( axis = 0; axis < nout; axis++  ) {
+               if( ( bitmask & mask ) == 0 ) ax[ nax++ ] = axis;
+               mask <<= 1;
+            }
+
+            pickfrm2 = astPickAxes( this, nax, ax, &junk );
+            junk = astAnnul( junk );
+            if( astIsARegion( pickfrm2 ) ) {
+
+/* See if either of these picked Regions can be simplified. */
+               sp1 = astSimplify( pickfrm1 );
+               sp2 = astSimplify( pickfrm2 );
+               if( (AstFrame *) sp1 != pickfrm1 ||
+                   (AstFrame *) sp2 != pickfrm2 ) {
+
+/* If so form a Prism containing the simplified Regions. */
+                  prism = astPrism( sp1, sp2, " ", status );
+
+/* Permute the axes of the Prism so that they are in the same order as
+   in the Box. */
+                  perm = astMalloc( sizeof( int )*nout );
+                  if( perm ) {
+
+                     for( i = 0; i < nout; i++ ) perm[ i ] = -1;
+
+                     for( i = 0; i < nax; i++ ) {
+                        perm[ ax[ i ] ] = i + ( nout - nax );
+                     }
+
+                     nax = 0;
+                     for( i = 0; i < nout; i++ ) {
+                        if( perm[ i ] == -1 ) perm[ i ] = nax++;
+                     }
+
+                     astPermAxes( prism, perm );
+                     perm = astFree( perm );
+                  }
+
+/* Put the original current Frame back in (in place of the CmpFrame
+   containined in the Prism). */
+                  frm = astGetFrame( this->frameset, AST__CURRENT );
+                  um = astUnitMap( nout, " ", status );
+                  newprism = astMapRegion( prism, um, frm );
+                  um = astAnnul( um );
+                  frm = astAnnul( frm );
+
+/* Attempt to simplify the Prism. */
+                  result = astSimplify( newprism );
+
+/* Free resources */
+                  prism = astAnnul( prism );
+                  newprism = astAnnul( newprism );
+               }
+
+               sp1 = astAnnul( sp1 );
+               sp2 = astAnnul( sp2 );
+            }
+            pickfrm2 = astAnnul( pickfrm2 );
+         }
+
+         pickfrm1 = astAnnul( pickfrm1 );
+      }
+
+      ax = astFree( ax );
+   }
+
+   map = astAnnul( map );
+
+/* If no Prism could be made, return a clone of the supplied Region
+   pointer. */
+   if( !result ) result = astClone( this );
+
+/* If an error occurred, annul the returned pointer. */
+   if ( !astOK ) result = astAnnul( result );
+
+/* Return the result. */
+   return result;
+}
+
+static void Decompose( AstMapping *this_mapping, AstMapping **map1,
+                       AstMapping **map2, int *series, int *invert1,
+                       int *invert2, int *status ) {
+/*
+*
+*  Name:
+*     Decompose
+
+*  Purpose:
+*     Decompose a Prism into two component Regions.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "cmpregion.h"
+*     void Decompose( AstMapping *this, AstMapping **map1,
+*                     AstMapping **map2, int *series,
+*                     int *invert1, int *invert2, int *status )
+
+*  Class Membership:
+*     Prism member function (over-rides the protected astDecompose
+*     method inherited from the Mapping class).
+
+*  Description:
+*     This function returns pointers to two Mappings which, when applied
+*     either in series or parallel, are equivalent to the supplied Mapping.
+*
+*     Since the Frame class inherits from the Mapping class, Frames can
+*     be considered as special types of Mappings and so this method can
+*     be used to decompose either CmpMaps, CmpFrames, CmpRegions or Prisms.
+
+*  Parameters:
+*     this
+*        Pointer to the Mapping.
+*     map1
+*        Address of a location to receive a pointer to first component
+*        Mapping.
+*     map2
+*        Address of a location to receive a pointer to second component
+*        Mapping.
+*     series
+*        Address of a location to receive a value indicating if the
+*        component Mappings are applied in series or parallel. A non-zero
+*        value means that the supplied Mapping is equivalent to applying map1
+*        followed by map2 in series. A zero value means that the supplied
+*        Mapping is equivalent to applying map1 to the lower numbered axes
+*        and map2 to the higher numbered axes, in parallel.
+*     invert1
+*        The value of the Invert attribute to be used with map1.
+*     invert2
+*        The value of the Invert attribute to be used with map2.
+*     status
+*        Pointer to the inherited status variable.
+
+*  Notes:
+*     - Any changes made to the component rames using the returned
+*     pointers will be reflected in the supplied CmpFrame.
+
+*-
+*/
+
+/* Local Variables: */
+   AstPrism *this;              /* Pointer to Prism structure */
+
+/* Check the global error status. */
+   if ( !astOK ) return;
+
+/* Obtain a pointer to the CmpMap structure. */
+   this = (AstPrism *) this_mapping;
+
+/* The components Frames of a Prism are considered to be parallel
+   Mappings. */
+   if( series ) *series = 0;
+
+/* The Frames are returned in their original order whether or not the
+   Prism has been inverted. */
+   if( map1 ) *map1 = astClone( this->region1 );
+   if( map2 ) *map2 = astClone( this->region2 );
+
+/* The invert flags dont mean anything for a Region, but we return them
+   anyway. If the Prism has been inverted, return inverted Invert flags. */
+   if( astGetInvert( this ) ) {
+      if( invert1 ) *invert1 = astGetInvert( this->region1 ) ? 0 : 1;
+      if( invert2 ) *invert2 = astGetInvert( this->region2 ) ? 0 : 1;
+
+/* If the Prism has not been inverted, return the current Invert flags. */
+   } else {
+      if( invert1 ) *invert1 = astGetInvert( this->region1 );
+      if( invert2 ) *invert2 = astGetInvert( this->region2 );
+   }
+}
+
+static int Equal( AstObject *this_object, AstObject *that_object, int *status ) {
+/*
+*  Name:
+*     Equal
+
+*  Purpose:
+*     Test if two Objects are equivalent.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     int Equal( AstObject *this_object, AstObject *that_object, int *status )
+
+*  Class Membership:
+*     Prism member function (over-rides the astEqual protected
+*     method inherited from the Region class).
+
+*  Description:
+*     This function returns a boolean result (0 or 1) to indicate whether
+*     two Prisms are equivalent.
+
+*  Parameters:
+*     this
+*        Pointer to the first Prism.
+*     that
+*        Pointer to the second Prism.
+*     status
+*        Pointer to the inherited status variable.
+
+*  Returned Value:
+*     One if the Prisms are equivalent, zero otherwise.
+
+*  Notes:
+*     - The Prisms are equivalent if their component Regions are
+*     equivalent and if they have the same boolean operation, negation
+*     and closed flags.
+*     - 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: */
+   AstPrism *that;
+   AstPrism *this;
+   int result;
+
+/* Initialise. */
+   result = 0;
+
+/* Check the global error status. */
+   if ( !astOK ) return result;
+
+/* Invoke the Equal method inherited from the parent Region class. This checks
+   that the Objects are both of the same class, and have the same Negated
+   and Closed flags (amongst other things). */
+   if( (*parent_equal)( this_object, that_object, status ) ) {
+
+/* Obtain pointers to the two Prism structures. */
+      this = (AstPrism *) this_object;
+      that = (AstPrism *) that_object;
+
+/* Test their first component Regions for equality. */
+      if( astEqual( this->region1, that->region1 ) ) {
+
+/* Test their second component Regions for equality. */
+         if( astEqual( this->region2, that->region2 ) ) result = 1;
+      }
+   }
+
+/* If an error occurred, clear the result value. */
+   if ( !astOK ) result = 0;
+
+/* Return the result, */
+   return result;
+}
+
+/*
+*  Name:
+*     MAKE_SET
+
+*  Purpose:
+*     Define a function to set an attribute value for a Prism.
+
+*  Type:
+*     Private macro.
+
+*  Synopsis:
+*     #include "prism.h"
+*     MAKE_SET(attribute,lattribute,type)
+
+*  Class Membership:
+*     Defined by the Prism class.
+
+*  Description:
+*     This macro expands to an implementation of a private member function
+*     of the form:
+*
+*        static void Set<Attribute>( AstRegion *this, <Type> value )
+*
+*     that sets the value of a specified Region attribute in the parent
+*     Region structure and also in the component Regions.
+
+*  Parameters:
+*     attribute
+*        Name of the attribute, as it appears in the function name.
+*     lattribute
+*        Name of the attribute, all in lower case.
+*     type
+*        The C type of the attribute.
+*/
+
+/* Define the macro. */
+#define MAKE_SET(attribute,lattribute,type) \
+static void Set##attribute( AstRegion *this_region, type value, int *status ) { \
+\
+/* Local Variables: */ \
+   AstPrism *this;         /* Pointer to the Prism structure */ \
+\
+/* Check the global error status. */ \
+   if ( !astOK ) return; \
+\
+/* Use the parent method to set the value in the parent Region structure. */ \
+   (*parent_set##lattribute)( this_region, value, status ); \
+\
+/* Also set the value in the two component Regions. */ \
+   this = (AstPrism *) this_region; \
+   astSet##attribute( this->region1, value ); \
+   astSet##attribute( this->region2, value ); \
+}
+
+/* Use the above macro to create accessors for the MeshSize and Closed
+   attributes. */
+MAKE_SET(MeshSize,meshsize,int)
+MAKE_SET(Closed,closed,int)
+
+/* Undefine the macro. */
+#undef MAKE_SET
+
+/*
+*  Name:
+*     MAKE_CLEAR
+
+*  Purpose:
+*     Define a function to clear an attribute value for a Prism.
+
+*  Type:
+*     Private macro.
+
+*  Synopsis:
+*     #include "prism.h"
+*     MAKE_CLEAR(attribute,lattribute)
+
+*  Class Membership:
+*     Defined by the Prism class.
+
+*  Description:
+*     This macro expands to an implementation of a private member function
+*     of the form:
+*
+*        static void Clear<Attribute>( AstRegion *this )
+*
+*     that sets the value of a specified Region attribute in the parent
+*     Region structure and also in the component Regions.
+
+*  Parameters:
+*     attribute
+*        Name of the attribute, as it appears in the function name.
+*     lattribute
+*        Name of the attribute, all in lower case.
+*/
+
+/* Define the macro. */
+#define MAKE_CLEAR(attribute,lattribute) \
+static void Clear##attribute( AstRegion *this_region, int *status ) { \
+\
+/* Local Variables: */ \
+   AstPrism *this;         /* Pointer to the Prism structure */ \
+\
+/* Check the global error status. */ \
+   if ( !astOK ) return; \
+\
+/* Use the parent method to clear the value in the parent Region structure. */ \
+   (*parent_clear##lattribute)( this_region, status ); \
+\
+/* Also clear the value in the two component Regions. */ \
+   this = (AstPrism *) this_region; \
+   astClear##attribute( this->region1 ); \
+   astClear##attribute( this->region2 ); \
+}
+
+/* Use the above macro to create accessors for the MeshSize and Closed
+   attributes. */
+MAKE_CLEAR(MeshSize,meshsize)
+MAKE_CLEAR(Closed,closed)
+
+/* Undefine the macro. */
+#undef MAKE_CLEAR
+
+static int GetObjSize( AstObject *this_object, int *status ) {
+/*
+*  Name:
+*     GetObjSize
+
+*  Purpose:
+*     Return the in-memory size of an Object.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     int GetObjSize( AstObject *this, int *status )
+
+*  Class Membership:
+*     Prism member function (over-rides the astGetObjSize protected
+*     method inherited from the parent class).
+
+*  Description:
+*     This function returns the in-memory size of the supplied Prism,
+*     in bytes.
+
+*  Parameters:
+*     this
+*        Pointer to the Prism.
+*     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: */
+   AstPrism *this;         /* Pointer to Prism structure */
+   int result;                /* Result value to return */
+
+/* Initialise. */
+   result = 0;
+
+/* Check the global error status. */
+   if ( !astOK ) return result;
+
+/* Obtain a pointers to the Prism structure. */
+   this = (AstPrism *) 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 );
+   result += astGetObjSize( this->region1 );
+   result += astGetObjSize( this->region2 );
+
+/* If an error occurred, clear the result value. */
+   if ( !astOK ) result = 0;
+
+/* Return the result, */
+   return result;
+}
+
+static int GetBounded( AstRegion *this_region, int *status ) {
+/*
+*  Name:
+*     GetBounded
+
+*  Purpose:
+*     Is the Region bounded?
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     int GetBounded( AstRegion *this, int *status )
+
+*  Class Membership:
+*     Prism method (over-rides the astGetBounded method inherited from
+*     the Region class).
+
+*  Description:
+*     This function returns a flag indicating if the Region is bounded.
+*     The implementation provided by the base Region class is suitable
+*     for Region sub-classes representing the inside of a single closed
+*     curve (e.g. Circle, Ellipse, Box, etc). Other sub-classes (such as
+*     Prism, PointList, etc ) may need to provide their own
+*     implementations.
+
+*  Parameters:
+*     this
+*        Pointer to the Region.
+*     status
+*        Pointer to the inherited status variable.
+
+*  Returned Value:
+*     Non-zero if the Region is bounded. Zero otherwise.
+
+*/
+
+/* Local Variables: */
+   AstPrism *this;            /* Pointer to Prism structure */
+   AstRegion *reg1;           /* Pointer to first component Region */
+   AstRegion *reg2;           /* Pointer to second component Region */
+   int neg;                   /* Negated flag to use with the Prism */
+   int reg1b;                 /* Is the first component Region bounded?*/
+   int reg2b;                 /* Is the second component Region bounded?*/
+   int result;                /* Returned result */
+
+/* Initialise */
+   result = 0;
+
+/* Check the global error status. */
+   if ( !astOK ) return result;
+
+/* Get a pointer to the Prism structure. */
+   this = (AstPrism *) this_region;
+
+/* Get the component Regions, and the Negated value for the Prism. The
+   returned Regions represent a region within the base Frame of the FrameSet
+   encapsulated by the parent Region structure. */
+   GetRegions( this, &reg1, &reg2, &neg, status );
+
+/* If the Prism has been inverted, temporarily invert the components. */
+   if( neg ) {
+      astNegate( reg1 );
+      astNegate( reg2 );
+   }
+
+/* See if either of the component Regions is bounded. */
+   reg1b = astGetBounded( reg1 );
+   reg2b = astGetBounded( reg2 );
+
+/* If the Prism has been inverted, re-invert the components to bring them
+   back to their original states. */
+   if( neg ) {
+      astNegate( reg1 );
+      astNegate( reg2 );
+   }
+
+/* The Prism is bounded only if both of the component Regions are bounded. */
+   result = ( reg1b && reg2b );
+
+/* Free resources. */
+   reg1 = astAnnul( reg1 );
+   reg2 = astAnnul( reg2 );
+
+/* Return zero if an error occurred. */
+   if( !astOK ) result = 0;
+
+/* Return the required pointer. */
+   return result;
+}
+
+static double GetFillFactor( AstRegion *this_region, int *status ) {
+/*
+*  Name:
+*     GetFillFactor
+
+*  Purpose:
+*     Obtain the value of the FillFactor attribute for a Prism.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     double GetFillFactor( AstRegion *this, int *status )
+
+*  Class Membership:
+*     Prism member function (over-rides the astGetFillFactor method inherited
+*     from the Region class).
+
+*  Description:
+*     This function returns the value of the FillFactor attribute for a
+*     Prism.  A suitable default value is returned if no value has
+*     previously been set.
+
+*  Parameters:
+*     this
+*        Pointer to the Prism.
+*     status
+*        Pointer to the inherited status variable.
+
+*  Returned Value:
+*     The FillFactor value to use.
+
+*/
+
+/* Local Variables: */
+   AstPrism *this;
+   double f1;
+   double f2;
+   double result;
+
+/* Check the global error status. */
+   if ( !astOK ) return AST__BAD;
+
+/* Initialise. */
+   result = AST__BAD;
+
+/* Obtain a pointer to the Prism structure. */
+   this = (AstPrism *) this_region;
+
+/* See if a FillFactor value has been set. If so, use the parent
+   astGetFillFactor  method to obtain it. */
+   if ( astTestFillFactor( this ) ) {
+      result = (*parent_getfillfactor)( this_region, status );
+
+/* Otherwise, we will generate a default value equal to the product of
+   the FillFactor values of the two component Regions. */
+   } else {
+      f1 = astGetFillFactor( this->region1 );
+      f2 = astGetFillFactor( this->region2 );
+      if( f1 != AST__BAD && f2 != AST__BAD ) result = f1*f2;
+   }
+
+/* If an error occurred, clear the returned value. */
+   if ( !astOK ) result = AST__BAD;
+
+/* Return the result. */
+   return result;
+}
+
+static void GetRegionBounds( AstRegion *this_region, double *lbnd,
+                             double *ubnd, int *status ){
+/*
+*
+*  Name:
+*     GetRegionBounds
+
+*  Purpose:
+*     Returns the bounding box of Prism.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "cmpregion.h"
+*     void GetRegionBounds( AstRegion *this_region, double *lbnd,
+*                           double *ubnd, int *status )
+
+*  Class Membership:
+*     Prism member function (over-rides the protected astGetRegionBounds
+*     method inherited from the Region class).
+
+*  Description:
+*     This function returns the upper and lower limits of a box which just
+*     encompasses the supplied Prism. The limits are returned as axis
+*     values within the Frame represented by the Prism. The value of the
+*     Negated attribute is ignored (i.e. it is assumed that the Prism has
+*     not been negated).
+
+*  Parameters:
+*     this
+*        Pointer to the Prism.
+*     lbnd
+*        Pointer to an array in which to return the lower axis bounds
+*        covered by the Prism. It should have at least as many elements as
+*        there are axes in the Prism. If an axis has no lower limit, the
+*        returned value will be the largest possible negative value.
+*     ubnd
+*        Pointer to an array in which to return the upper axis bounds
+*        covered by the Prism. It should have at least as many elements as
+*        there are axes in the Prism. If an axis has no upper limit, the
+*        returned value will be the largest possible positive value.
+
+*  Notes:
+*    - The value of the Negated attribute is ignored (i.e. it is assumed that
+*    the Prism has not been negated).
+*    - If an axis has no extent on an axis then the lower limit will be
+*    returned larger than the upper limit. Note, this is different to an
+*    axis which has a constant value (in which case both lower and upper
+*    limit will be returned set to the constant value).
+*    - If the bounds on an axis cannot be determined, AST__BAD is returned for
+*    both upper and lower bounds
+*    - The implementation of this method for Prisms attempts to split the Prism
+*    into two separate Regions spanning indepenent sets of axes, and then uses
+*    the astGetRegionBouinds method to get the bounds on these two Regions. Care
+*    has to be taken because the Prism may have been remapped into a different
+*    Frame since it was created.
+
+*-
+*/
+
+/* Local Variables: */
+   AstFrame *cfrm1;             /* Frame spanning current axes for 1st component Region */
+   AstFrame *cfrm2;             /* Frame spanning current axes for 2nd component Region */
+   AstFrame *cfrm;              /* Current Frame for total Prism */
+   AstMapping *map1;            /* Base->Current Mapping for axes of 1st component Region */
+   AstMapping *map2;            /* Base->Current Mapping for axes of 2nd component Region */
+   AstMapping *map;             /* Case->Current mapping for total Prism */
+   AstPrism *this;              /* Pointer to Prism structure */
+   AstRegion *reg1;             /* 1st component Region Mapping into Prism's Frame */
+   AstRegion *reg2;             /* 2nd component Region Mapping into Prism's Frame */
+   int *baxes;                  /* Indicies of Base Frame axes to be picked */
+   int *caxes;                  /* Indicies of Current Frame axes to be picked */
+   int iax;                     /* Axis index */
+   int nax1;                    /* Number of axes in first component Region */
+   int nax1_out;                /* Number of current Frame axes in first component Region */
+   int nax2;                    /* Number of axes in second component Region */
+
+/* Check the global error status. */
+   if ( !astOK ) return;
+
+/* Obtain a pointer to the Prism structure. */
+   this = (AstPrism *) this_region;
+
+/* Initialise */
+   cfrm1 = NULL;
+   cfrm2 = NULL;
+   map1 = NULL;
+   map2 = NULL;
+   nax1_out = 0;
+
+/* The number of base-frame axes spanned by the two component Regions. */
+   nax1 = astGetNaxes( this->region1 );
+   nax2 = astGetNaxes( this->region2 );
+
+/* Work space to hold the base frame indices for a single component
+   FrameSet. */
+   baxes = astMalloc( ( nax1 + nax2 )*sizeof( int ) );
+   if( astOK ) {
+
+/* Get the Mapping from Base to Current Frame from the Prism's FrameSet,
+   and get a pointer to the current Frame. */
+      map = astGetMapping( this_region->frameset, AST__BASE, AST__CURRENT );
+      cfrm = astGetFrame( this_region->frameset, AST__CURRENT );
+
+/* Attempt to split the FrameSet encapsulated within the Prism into two -
+   one containing the axes spanned by the first component Region and
+   another containing the axes spanned by the second component Region.
+   First store the zero-based indices of the base Frame axes
+   corresponding to the first component Region. */
+      for( iax = 0; iax < nax1; iax++ ) baxes[ iax ] = iax;
+
+/* Attempt to split these inputs from the total Mapping, thus creating a
+   Mapping that converts just the axes spanned by the first component
+   Region. */
+      caxes = astMapSplit( map, nax1, baxes, &map1 );
+
+/* If the Mapping could be split, get a Frame spanning the current Frame
+   axes corresponding to the first component Region. */
+      if( caxes ) {
+         nax1_out = astGetNout( map1 );
+         cfrm1 = astPickAxes( cfrm, nax1_out, caxes, NULL );
+         caxes = astFree( caxes );
+      }
+
+/* Do the same thing for the second component Region. */
+      for( iax = 0; iax < nax2; iax++ ) baxes[ iax ] = iax + nax1;
+      caxes = astMapSplit( map, nax2, baxes, &map2 );
+      if( caxes ) {
+         cfrm2 = astPickAxes( cfrm, astGetNout( map2 ), caxes, NULL );
+         caxes = astFree( caxes );
+      }
+
+/* Free resources. */
+      cfrm = astAnnul( cfrm );
+      map = astAnnul( map );
+   }
+   baxes = astFree( baxes );
+
+/* If the Prism mapping could not be split, use the parent GetRegionBounds
+   method. */
+   if( !map1 || !map2 ) {
+      (*parent_getregionbounds)( this_region, lbnd, ubnd, status );
+
+/* Otherwise, we get the bounds of the two component Regions separately. */
+   } else {
+
+/* Remap the first component Region using the FrameSet created above. */
+      reg1 = astMapRegion( this->region1, map1, cfrm1 );
+
+/* Get the bounds of this Region, storing the results at the start of the
+   returned lbnd/ubnd arrays. */
+      astGetRegionBounds( reg1, lbnd, ubnd );
+      reg1 = astAnnul( reg1 );
+
+/* Do the same thing for the second component Region, storing the results
+   at the end of the returned lbnd/ubnd arrays. */
+      reg2 = astMapRegion( this->region2, map2, cfrm2 );
+      astGetRegionBounds( reg2, lbnd + nax1_out, ubnd + nax1_out );
+      reg2 = astAnnul( reg2 );
+
+/* What about the possibility that the axes of the Prism have been
+   permuted? */
+
+   }
+
+/* Free resources. */
+   if( map1 ) map1 = astAnnul( map1 );
+   if( map2 ) map2 = astAnnul( map2 );
+   if( cfrm1 ) cfrm1 = astAnnul( cfrm1 );
+   if( cfrm2 ) cfrm2 = astAnnul( cfrm2 );
+
+}
+
+static void GetRegions( AstPrism *this, AstRegion **reg1, AstRegion **reg2,
+                        int *neg, int *status ) {
+/*
+*
+*  Name:
+*     GetRegions
+
+*  Purpose:
+*     Get the component Regions of a Prism.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "region.h"
+*     void GetRegions( AstPrism *this, AstRegion **reg1, AstRegion **reg2,
+*                      int *neg, int *status )
+
+*  Class Membership:
+*     Prism member function
+
+*  Description:
+*     This function returns pointers to the two Regions in a Prism, together
+*     with the Negated flag for the Prism.
+*
+*     The current Frames in both the returned component Regions will be
+*     equivalent to componets of the base Frame in the FrameSet encapsulated
+*     by the parent Region structure.
+
+*  Parameters:
+*     this
+*        Pointer to the Prism.
+*     reg1
+*        Address of a location to receive a pointer to first component
+*        Region. This is the region which is to be extruded.
+*     reg2
+*        Address of a location to receive a pointer to second component
+*        Region. This will be an Interval defining the axes along which
+*        the first Region is to be extruded.
+*     neg
+*        Pointer to an int in which to return the value of the Negated
+*        attribute of the Prism.
+*     status
+*        Pointer to the inherited status variable.
+
+*  Notes:
+*     - The returned pointers should be annuled using astAnnul when no
+*     longer needed.
+*     - The Frames represented by the returned Regions (that is, the
+*     current Frames in their encapsulated FrameSets) are equivalent to the
+*     base Frame in the FrameSet encapsulated within the parent Region.
+*     - Any changes made to the component Regions using the returned
+*     pointers will be reflected in the supplied Prism.
+
+*-
+*/
+
+/* Initialise */
+   if( reg1 ) *reg1 = NULL;
+   if( reg2 ) *reg2 = NULL;
+
+/* Check the global error status. */
+   if ( !astOK ) return;
+
+/* Store the required values.*/
+   *reg1 = astClone( this->region1 );
+   *reg2 = astClone( this->region2 );
+   *neg = astGetNegated( (AstRegion *) this );
+}
+
+static AstRegion *GetDefUnc( AstRegion *this_region, int *status ) {
+/*
+*  Name:
+*     GetDefUnc
+
+*  Purpose:
+*     Obtain a pointer to the default uncertainty Region for a given Region.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     AstRegion *GetDefUnc( AstRegion *this )
+
+*  Class Membership:
+*     Prism method (over-rides the astGetDefUnc method inherited from
+*     the Region class).
+
+*     This function returns a pointer to a Region which represents the
+*     default uncertainty associated with a position on the boundary of the
+*     given  Region. The returned Region refers to the base Frame within the
+*     FrameSet encapsulated by the supplied Region.
+
+*  Parameters:
+*     this
+*        Pointer to the Region.
+
+*  Returned Value:
+*     A pointer to the Region. This should be annulled (using astAnnul)
+*     when no longer needed.
+
+*  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: */
+   AstPrism *this;            /* Pointer to Prism structure */
+   AstRegion *bunc1;          /* Uncertainty Region for 1st component */
+   AstRegion *bunc2;          /* Uncertainty Region for 2nd component */
+   AstRegion *result;         /* Returned pointer */
+
+/* Initialise */
+   result = NULL;
+
+/* Check the global error status. */
+   if ( !astOK ) return result;
+
+/* Get a pointer to the Prism structure. */
+   this = (AstPrism *) this_region;
+
+/* Construct a default uncertainty Region from the uncertainty Regions
+   in the two component Regions. The current Frames in the component
+   Regions are equivalent to the base Frame in the parent Region structure.
+   So we may need to map the component uncertainty into the current Region of
+   the parent if required later on. */
+   bunc1 = astGetUncFrm( this->region1, AST__CURRENT );
+   bunc2 = astGetUncFrm( this->region2, AST__CURRENT );
+
+/* Combine them into a Prism. */
+   result = (AstRegion *) astPrism( bunc1, bunc2, "", status );
+
+/* Free resources. */
+   bunc1 = astAnnul( bunc1 );
+   bunc2 = astAnnul( bunc2 );
+
+/* Return NULL if an error occurred. */
+   if( !astOK ) result = astAnnul( result );
+
+/* Return the required pointer. */
+   return result;
+}
+
+void astInitPrismVtab_(  AstPrismVtab *vtab, const char *name, int *status ) {
+/*
+*+
+*  Name:
+*     astInitPrismVtab
+
+*  Purpose:
+*     Initialise a virtual function table for a Prism.
+
+*  Type:
+*     Protected function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     void astInitPrismVtab( AstPrismVtab *vtab, const char *name )
+
+*  Class Membership:
+*     Prism vtab initialiser.
+
+*  Description:
+*     This function initialises the component of a virtual function
+*     table which is used by the Prism 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 */
+   AstFrameVtab *frame;          /* Pointer to Frame component of Vtab */
+   AstMappingVtab *mapping;      /* Pointer to Mapping component of Vtab */
+   AstObjectVtab *object;        /* Pointer to Object component of Vtab */
+   AstRegionVtab *region;        /* Pointer to Region 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. */
+   astInitRegionVtab( (AstRegionVtab *) vtab, name );
+
+/* Store a unique "magic" value in the virtual function table. This
+   will be used (by astIsAPrism) 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 = &(((AstRegionVtab *) vtab)->id);
+
+/* Initialise member function pointers. */
+/* ------------------------------------ */
+/* Store pointers to the member functions (implemented here) that
+   provide virtual methods for this class. */
+
+/* None. */
+
+/* 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;
+   region = (AstRegionVtab *) vtab;
+   frame = (AstFrameVtab *) vtab;
+
+   parent_getobjsize = object->GetObjSize;
+   object->GetObjSize = GetObjSize;
+
+#if defined(THREAD_SAFE)
+   parent_managelock = object->ManageLock;
+   object->ManageLock = ManageLock;
+#endif
+
+   parent_transform = mapping->Transform;
+   mapping->Transform = Transform;
+
+   parent_simplify = mapping->Simplify;
+   mapping->Simplify = Simplify;
+
+   parent_maplist = mapping->MapList;
+   mapping->MapList = MapList;
+
+   parent_getdefunc = region->GetDefUnc;
+   region->GetDefUnc = GetDefUnc;
+
+   parent_setregfs = region->SetRegFS;
+   region->SetRegFS = SetRegFS;
+
+   parent_equal = object->Equal;
+   object->Equal = Equal;
+
+   parent_clearclosed = region->ClearClosed;
+   region->ClearClosed = ClearClosed;
+
+   parent_clearmeshsize = region->ClearMeshSize;
+   region->ClearMeshSize = ClearMeshSize;
+
+   parent_setclosed = region->SetClosed;
+   region->SetClosed = SetClosed;
+
+   parent_setmeshsize = region->SetMeshSize;
+   region->SetMeshSize = SetMeshSize;
+
+   parent_getfillfactor = region->GetFillFactor;
+   region->GetFillFactor = GetFillFactor;
+
+   parent_overlapx = region->OverlapX;
+   region->OverlapX = OverlapX;
+
+   parent_regsetattrib = region->RegSetAttrib;
+   region->RegSetAttrib = RegSetAttrib;
+
+   parent_regclearattrib = region->RegClearAttrib;
+   region->RegClearAttrib = RegClearAttrib;
+
+   parent_getregionbounds = region->GetRegionBounds;
+   region->GetRegionBounds = GetRegionBounds;
+
+/* Store replacement pointers for methods which will be over-ridden by
+   new member functions implemented here. */
+   mapping->Decompose = Decompose;
+   region->RegBaseBox = RegBaseBox;
+   region->RegBaseMesh = RegBaseMesh;
+   region->RegPins = RegPins;
+   region->GetBounded = GetBounded;
+   region->RegCentre = RegCentre;
+   region->Overlap = Overlap;
+   region->RegBasePick = RegBasePick;
+
+/* Declare the copy constructor, destructor and class dump function. */
+   astSetCopy( vtab, Copy );
+   astSetDelete( vtab, Delete );
+   astSetDump( vtab, Dump, "Prism", "Region extrusion into higher dimensions" );
+
+/* 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) );
+   }
+}
+
+#if defined(THREAD_SAFE)
+static int ManageLock( AstObject *this_object, int mode, int extra,
+                       AstObject **fail, int *status ) {
+/*
+*  Name:
+*     ManageLock
+
+*  Purpose:
+*     Manage the thread lock on an Object.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "object.h"
+*     AstObject *ManageLock( AstObject *this, int mode, int extra,
+*                            AstObject **fail, int *status )
+
+*  Class Membership:
+*     CmpMap member function (over-rides the astManageLock protected
+*     method inherited from the parent class).
+
+*  Description:
+*     This function manages the thread lock on the supplied Object. The
+*     lock can be locked, unlocked or checked by this function as
+*     deteremined by parameter "mode". See astLock for details of the way
+*     these locks are used.
+
+*  Parameters:
+*     this
+*        Pointer to the Object.
+*     mode
+*        An integer flag indicating what the function should do:
+*
+*        AST__LOCK: Lock the Object for exclusive use by the calling
+*        thread. The "extra" value indicates what should be done if the
+*        Object is already locked (wait or report an error - see astLock).
+*
+*        AST__UNLOCK: Unlock the Object for use by other threads.
+*
+*        AST__CHECKLOCK: Check that the object is locked for use by the
+*        calling thread (report an error if not).
+*     extra
+*        Extra mode-specific information.
+*     fail
+*        If a non-zero function value is returned, a pointer to the
+*        Object that caused the failure is returned at "*fail". This may
+*        be "this" or it may be an Object contained within "this". Note,
+*        the Object's reference count is not incremented, and so the
+*        returned pointer should not be annulled. A NULL pointer is
+*        returned if this function returns a value of zero.
+*     status
+*        Pointer to the inherited status variable.
+
+*  Returned Value:
+*    A local status value:
+*        0 - Success
+*        1 - Could not lock or unlock the object because it was already
+*            locked by another thread.
+*        2 - Failed to lock a POSIX mutex
+*        3 - Failed to unlock a POSIX mutex
+*        4 - Bad "mode" value supplied.
+
+*  Notes:
+*     - This function attempts to execute even if an error has already
+*     occurred.
+*/
+
+/* Local Variables: */
+   AstPrism *this;       /* Pointer to Prism structure */
+   int result;           /* Returned status value */
+
+/* Initialise */
+   result = 0;
+
+/* Check the supplied pointer is not NULL. */
+   if( !this_object ) return result;
+
+/* Obtain a pointers to the Prism structure. */
+   this = (AstPrism *) this_object;
+
+/* Invoke the ManageLock method inherited from the parent class. */
+   if( !result ) result = (*parent_managelock)( this_object, mode, extra,
+                                                fail, status );
+
+/* Invoke the astManageLock method on any Objects contained within
+   the supplied Object. */
+   if( !result ) result = astManageLock( this->region1, mode, extra, fail );
+   if( !result ) result = astManageLock( this->region2, mode, extra, fail );
+
+   return result;
+
+}
+#endif
+
+static int MapList( AstMapping *this_mapping, int series, int invert,
+                    int *nmap, AstMapping ***map_list, int **invert_list,
+                    int *status ) {
+/*
+*  Name:
+*     MapList
+
+*  Purpose:
+*     Decompose a Prism into a sequence of simpler Regions.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "mapping.h"
+*     int MapList( AstMapping *this, int series, int invert, int *nmap,
+*                  AstMapping ***map_list, int **invert_list )
+
+*  Class Membership:
+*     Prism member function (over-rides the protected astMapList
+*     method inherited from the Region class).
+
+*  Description:
+*     This function decomposes a Prism into a sequence of simpler
+*     Regions which may be applied in parallel to achieve the same
+*     effect. The Prism is decomposed as far as possible, but it is
+*     not guaranteed that this will necessarily yield any more than
+*     one Region, which may actually be the original Prism supplied.
+
+*  Parameters:
+*     this
+*        Pointer to the Prism to be decomposed (the Prism is not
+*        actually modified by this function).
+*     series
+*        Prisms always apply their component Regions in parallel, so this
+*        value should always be zero. This function will return without
+*        action if it is non-zero.
+*     invert
+*        Inverting a Region has no effect on the properties of the Region
+*        and so this parameter is ignored.
+*     nmap
+*        The address of an int which holds a count of the number of
+*        individual Regions in the decomposition. On entry, this
+*        should count the number of Regions already in the
+*        "*map_list" array (below). On exit, it is updated to include
+*        any new Regions appended by this function.
+*     map_list
+*        Address of a pointer to an array of Region pointers. On
+*        entry, this array pointer should either be NULL (if no
+*        Regions have yet been obtained) or should point at a
+*        dynamically allocated array containing Region pointers
+*        ("*nmap" in number) which have been obtained from a previous
+*        invocation of this function.
+*
+*        On exit, the dynamic array will be enlarged to contain any
+*        new Region pointers that result from the decomposition
+*        requested. These pointers will be appended to any previously
+*        present, and the array pointer will be updated as necessary
+*        to refer to the enlarged array (any space released by the
+*        original array will be freed automatically).
+*
+*        The new Region pointers returned will identify a sequence of
+*        Regions which, when applied (in parallel) in order, will be
+*        equivalent to the original Prism.
+*
+*        All the Region pointers returned by this function should be
+*        annulled by the caller, using astAnnul, when no longer
+*        required. The dynamic array holding these pointers should
+*        also be freed, using astFree.
+*     invert_list
+*        Address of a pointer to an array of int. On entry, this array
+*        pointer should either be NULL (if no Regions have yet been
+*        obtained) or should point at a dynamically allocated array
+*        containing Invert attribute values ("*nmap" in number) which
+*        have been obtained from a previous invocation of this
+*        function.
+*
+*        On exit, the dynamic array will be enlarged to contain any
+*        new Invert attribute values that result from the
+*        decomposition requested. These values will be appended to any
+*        previously present, and the array pointer will be updated as
+*        necessary to refer to the enlarged array (any space released
+*        by the original array will be freed automatically).
+*
+*        The new Invert values returned will always be zero since a
+*        Region is unaffected by its Invert setting.
+*
+*        The dynamic array holding these values should be freed by the
+*        caller, using astFree, when no longer required.
+
+*  Returned Value:
+*     Zero is always returned.
+
+*  Notes:
+*     - It is unspecified to what extent the original Prism and the
+*     individual (decomposed) Regions are
+*     inter-dependent. Consequently, the individual Regions cannot be
+*     modified without risking modification of the original Prism.
+*     - If this function is invoked with the global error status set,
+*     or if it should fail for any reason, then the *nmap value, the
+*     list of Region pointers and the list of Invert values will all
+*     be returned unchanged.
+*/
+
+/* Local Variables: */
+   AstPrism *this;              /* Pointer to Prism structure */
+
+/* Check the global error status. */
+   if ( !astOK ) return 0;
+
+/* Obtain a pointer to the Prism structure. */
+   this = (AstPrism *) this_mapping;
+
+/* When considered as a CmpMap, a Prism always combines its component
+   Mappings (Regions) in parallel. So check that a parallel decomposition
+   was requested. */
+   if ( ! series ) {
+
+/* Concatenate the Mapping lists obtained from each component Region. */
+      (void) astMapList( (AstMapping *) this->region1, 0, 0, nmap, map_list,
+                         invert_list );
+      (void) astMapList( (AstMapping *) this->region2, 0, 0, nmap, map_list,
+                         invert_list );
+
+/* If the Prism does not combine its components in the way required
+   by the decomposition (series or parallel), then we cannot decompose
+   it. In this case it must be appended to the Mapping list as a
+   single entity. We can use the parent class method to do this. */
+   } else {
+      (void) ( *parent_maplist )( this_mapping, series, invert, nmap,
+                                  map_list, invert_list, status );
+   }
+
+   return 0;
+}
+
+static int Overlap( AstRegion *this, AstRegion *that, int *status ){
+/*
+*  Name:
+*     Overlap
+
+*  Purpose:
+*     Test if two regions overlap each other.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     int Overlap( AstRegion *this, AstRegion *that, int *status )
+
+*  Class Membership:
+*     Prism member function (over-rides the astOverlap method inherited
+*     from the Region class).
+
+*  Description:
+*     This function returns an integer value indicating if the two
+*     supplied Regions overlap. The two Regions are converted to a commnon
+*     coordinate system before performing the check. If this conversion is
+*     not possible (for instance because the two Regions represent areas in
+*     different domains), then the check cannot be performed and a zero value
+*     is returned to indicate this.
+
+*  Parameters:
+*     this
+*        Pointer to the first Region.
+*     that
+*        Pointer to the second Region.
+*     status
+*        Pointer to the inherited status variable.
+
+*  Returned Value:
+*     astOverlap()
+*        A value indicating if there is any overlap between the two Regions.
+*        Possible values are:
+*
+*        0 - The check could not be performed because the second Region
+*            could not be mapped into the coordinate system of the first
+*            Region.
+*
+*        1 - There is no overlap between the two Regions.
+*
+*        2 - The first Region is completely inside the second Region.
+*
+*        3 - The second Region is completely inside the first Region.
+*
+*        4 - There is partial overlap between the two Regions.
+*
+*        5 - The Regions are identical.
+*
+*        6 - The second Region is the negation of the first Region.
+
+*  Notes:
+*     - The returned values 5 and 6 do not check the value of the Closed
+*     attribute in the two Regions.
+*     - A value of zero will be returned if this function is invoked with the
+*     AST error status set, or if it should fail for any reason.
+
+*/
+
+/* Local Variables: */
+   AstFrame *bfrm;
+   AstFrame *efrm;
+   AstFrameSet *fs;
+   AstMapping *bmap;
+   AstMapping *emap;
+   AstMapping *map1;
+   AstMapping *map2;
+   AstMapping *map;
+   AstMapping *smap;
+   AstRegion *that_base2;
+   AstRegion *that_base;
+   AstRegion *that_ext2;
+   AstRegion *that_ext;
+   AstRegion *this_reg1;
+   AstRegion *this_reg2;
+   int *inax;
+   int *outax;
+   int i;
+   int nbase;
+   int next;
+   int rbase;
+   int result;
+   int rext;
+   int that_neg;
+   int this_neg;
+
+/* A table indicating how to combine together the overlap state of the
+   extrusion Regions with the overlap state of the other (base) Region.
+   The first index represents the value returned by the astOverlap method
+   when used to determine the overlap of the base Regions in the two
+   supplied Prisms. The second index represents the value returned by the
+   astOverlap method when used to determine the overlap of the extrusion
+   Regions in the two supplied Prisms. The integer values stored in the
+   array represent the astOverlap value describing the overlap of the two
+   Prisms. */
+   static int rtable[ 7 ][ 7 ] = { { 0, 0, 0, 0, 0, 0, 0 },
+                                   { 0, 1, 1, 1, 1, 1, 1 },
+                                   { 0, 1, 2, 4, 4, 2, 1 },
+                                   { 0, 1, 4, 3, 4, 3, 1 },
+                                   { 0, 1, 4, 4, 4, 4, 1 },
+                                   { 0, 1, 2, 3, 4, 5, 1 },
+                                   { 0, 1, 1, 1, 1, 1, 6 } };
+
+/* Initialise */
+   result = 0;
+
+/* Check the inherited status. */
+   if ( !astOK ) return result;
+
+/* Get pointers to the base and extrusion Regions within "this", and also
+   the nagated flag. */
+   GetRegions( (AstPrism *) this, &this_reg1, &this_reg2, &this_neg, status );
+
+/* Get the number of axes in the base and extrusion Regions of "this". */
+   nbase = astGetNaxes( this_reg1 );
+   next = astGetNaxes( this_reg2 );
+
+/* Get a FrameSet which goes from the Frame represented by "this" to the
+   Frame represented by "that". Check that the conection is defined. */
+   fs = astConvert( this, that, "" );
+   if( fs ) {
+
+/* Get the forward Mapping from the above FrameSet. */
+      map2 = astGetMapping( fs, AST__BASE, AST__CURRENT );
+
+/* Get a pointer to the Mapping from base to current Frame in "this". */
+      map1 = astGetMapping( this->frameset, AST__BASE, AST__CURRENT );
+
+/* Combine these Mappings to get the Mapping from the base Frame of "this"
+   to the current Frame of "that". */
+      map = (AstMapping *) astCmpMap( map1, map2, 1, "", status );
+
+/* Simplify this Mapping. */
+      smap = astSimplify( map );
+
+/* See if the extrusion axes in "this" correspond to a unique set of axes
+   in the current Frame of "that". */
+      inax = astMalloc( sizeof(int)*(size_t)next );
+      for( i = 0; i < next; i++ ) inax[ i ] = nbase + i;
+      outax = astMapSplit( smap, next, inax, &emap );
+
+/* If they do, attempt to create a Region by picking the axes from "that"
+   that correspond to the extrusion axes in "this". */
+      if( emap && astGetNout( emap ) == next ) {
+         that_ext = (AstRegion *) astPickAxes( that, next, outax, NULL );
+
+/* If the picked axes formed a Region, see if the base axes can also be
+   picked in the same way. */
+         if( astIsARegion( that_ext ) ) {
+            outax = astFree( outax );
+            inax = astGrow( inax, (size_t)nbase, sizeof( int ) );
+            for( i = 0; i < nbase; i++ ) inax[ i ] = i;
+            outax = astMapSplit( smap, nbase, inax, &bmap );
+            if( bmap && astGetNout( bmap ) == nbase ) {
+               that_base = (AstRegion *) astPickAxes( that, nbase, outax, NULL );
+               if( astIsARegion( that_base ) ) {
+
+/* Map the two Regions picked from "that" into the Frames of the two
+   sub-regions within "this". */
+                  astInvert( emap );
+                  efrm = astGetFrame( this_reg2->frameset, AST__CURRENT );
+                  that_ext2 = astMapRegion( that_ext, emap, efrm );
+
+                  astInvert( bmap );
+                  bfrm = astGetFrame( this_reg1->frameset, AST__CURRENT );
+                  that_base2 = astMapRegion( that_base, bmap, bfrm );
+
+/* We can test separately for overlap of the two extrusion Regions, and for
+   overlap of the two base Regions, and then combine the returned flags to
+   represent overlap of the whole Prism. */
+                  rbase = astOverlap( this_reg1, that_base2 );
+                  rext = astOverlap( this_reg2, that_ext2 );
+                  result = rtable[ rbase ][ rext ];
+
+/* The values in the rtable array assume that neither of the supplied
+   Prisms have been negated. Modify the value obtained from rtable to
+   take account of negation of either or both of the supplied Prisms. */
+                  that_neg = astGetNegated( that );
+                  if( this_neg ) {
+                     if( that_neg ) {
+                        if( result == 1 ) {
+                           result = 4;
+                        } else if( result == 2 ) {
+                           result = 3;
+                        } else if( result == 3 ) {
+                           result = 2;
+                        }
+                     } else {
+                        if( result == 1 ) {
+                           result = 3;
+                        } else if( result == 2 ) {
+                           result = 4;
+                        } else if( result == 3 ) {
+                           result = 1;
+                        } else if( result == 5 ) {
+                           result = 6;
+                        } else if( result == 6 ) {
+                           result = 5;
+                        }
+                     }
+                  } else if( that_neg ){
+                     if( result == 1 ) {
+                        result = 2;
+                     } else if( result == 2 ) {
+                        result = 1;
+                     } else if( result == 3 ) {
+                        result = 4;
+                     } else if( result == 5 ) {
+                        result = 6;
+                     } else if( result == 6 ) {
+                        result = 5;
+                     }
+                  }
+
+/* Free resources */
+                  efrm = astAnnul( efrm );
+                  that_ext2 = astAnnul( that_ext2 );
+                  bfrm = astAnnul( bfrm );
+                  that_base2 = astAnnul( that_base2 );
+               }
+               that_base = astAnnul( that_base );
+               bmap = astAnnul( bmap );
+            }
+         }
+         emap = astAnnul( emap );
+         that_ext = astAnnul( that_ext );
+      }
+      outax = astFree( outax );
+      inax = astFree( inax );
+      smap = astAnnul( smap );
+      map = astAnnul( map );
+      map1 = astAnnul( map1 );
+      map2 = astAnnul( map2 );
+      fs = astAnnul( fs );
+   }
+   this_reg1 = astAnnul( this_reg1 );
+   this_reg2 = astAnnul( this_reg2 );
+
+/* If overlap could not be determined using the above implementation, try
+   using the implementation inherited from the parent Region class. Use
+   OverlapX rather than Overlap since a) it is OverlapX that does the work,
+   and b) calling Overlap could end us in an infinite loop. */
+   if( !result ) result = (*parent_overlapx)( this, that, status );
+
+/* If not OK, return zero. */
+   if( !astOK ) result = 0;
+
+/* Return the result. */
+   return result;
+}
+
+static int OverlapX( AstRegion *that, AstRegion *this, int *status ){
+/*
+*  Name:
+*     OverlapX
+
+*  Purpose:
+*     Test if two regions overlap each other.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     int OverlapX( AstRegion *that, AstRegion *this )
+
+*  Class Membership:
+*     Prism member function (over-rides the astOverlapX method inherited
+*     from the Region class).
+
+*  Description:
+*     This function performs the processing for the public astOverlap
+*     method and has exactly the same interface except that the order
+*     of the two arguments is swapped. This is a trick to allow
+*     the astOverlap method to be over-ridden by derived classes on
+*     the basis of the class of either of its two arguments.
+*
+*     See the astOverlap method for details of the interface.
+*/
+
+/* Local Variables; */
+   int result;
+
+/* Check the global error status. */
+   if ( !astOK ) return 0;
+
+/* We know that "that" is a Prism, so call the private Overlap method,
+   and then modify the returned value to take account of the fact that the
+   two Regions are swapped. */
+   result = Overlap( that, this, status );
+
+   if( result == 2 ){
+      result = 3;
+   } else if( result == 3 ){
+      result = 2;
+   }
+
+   return result;
+}
+
+
+static void RegBaseBox( AstRegion *this_region, double *lbnd, double *ubnd,
+                        int *status ){
+/*
+*  Name:
+*     RegBaseBox
+
+*  Purpose:
+*     Returns the bounding box of an un-negated Region in the base Frame of
+*     the encapsulated FrameSet.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     void RegBaseBox( AstRegion *this, double *lbnd, double *ubnd,
+*                      int *status )
+
+*  Class Membership:
+*     Prism member function (over-rides the astRegBaseBox protected
+*     method inherited from the Region class).
+
+*  Description:
+*     This function returns the upper and lower axis bounds of a Region in
+*     the base Frame of the encapsulated FrameSet, assuming the Region
+*     has not been negated. That is, the value of the Negated attribute
+*     is ignored.
+
+*  Parameters:
+*     this
+*        Pointer to the Region.
+*     lbnd
+*        Pointer to an array in which to return the lower axis bounds
+*        covered by the Region in the base Frame of the encapsulated
+*        FrameSet. It should have at least as many elements as there are
+*        axes in the base Frame.
+*     ubnd
+*        Pointer to an array in which to return the upper axis bounds
+*        covered by the Region in the base Frame of the encapsulated
+*        FrameSet. It should have at least as many elements as there are
+*        axes in the base Frame.
+*     status
+*        Pointer to the inherited status variable.
+
+*/
+
+/* Local Variables: */
+   AstPrism *this;              /* Pointer to Prism structure */
+   AstRegion *reg1;             /* Pointer to first component Region */
+   AstRegion *reg2;             /* Pointer to second component Region */
+   int nax;                     /* Number of axes in Frame */
+   int neg;                     /* Negated flag for Prism */
+
+/* Check the global error status. */
+   if ( !astOK ) return;
+
+/* Get a pointer to the Prism structure */
+   this = (AstPrism *) this_region;
+
+/* Get pointers to the component Regions. */
+   GetRegions( this, &reg1, &reg2, &neg, status );
+
+/* The base Frame of the parent Region structure is equivalent to a
+   CmpFrame containing the current Frames of the component Regions.
+   Get the no. of axes in the first component Frame. */
+   nax = astGetNaxes( reg1 );
+
+/* Get the bounding boxes of the component Regions in these Frame,
+   storing the values in the supplied arrays. */
+   astGetRegionBounds( reg1, lbnd, ubnd );
+   astGetRegionBounds( reg2, lbnd + nax, ubnd + nax );
+
+/* Free resources.*/
+   reg1 = astAnnul( reg1 );
+   reg2 = astAnnul( reg2 );
+}
+
+static AstPointSet *RegBaseMesh( AstRegion *this_region, int *status ){
+/*
+*  Name:
+*     RegBaseMesh
+
+*  Purpose:
+*     Return a PointSet containing a mesh of points on the boundary of a
+*     Region in its base Frame.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     AstPointSet *RegBaseMesh( AstRegion *this, int *status )
+
+*  Class Membership:
+*     Prism member function (over-rides the astRegBaseMesh protected
+*     method inherited from the Region class).
+
+*  Description:
+*     This function returns a PointSet containing a mesh of points on the
+*     boundary of the Region. The points refer to the base Frame of
+*     the encapsulated FrameSet.
+
+*  Parameters:
+*     this
+*        Pointer to the Region.
+*     status
+*        Pointer to the inherited status variable.
+
+*  Returned Value:
+*     Pointer to the PointSet. Annul the pointer using astAnnul when it
+*     is no longer needed.
+
+*  Notes:
+*    - A NULL pointer is returned if an error has already occurred, or if
+*    this function should fail for any reason.
+
+*/
+
+
+/* Local Variables: */
+   AstPointSet *grid1;            /* PointSet holding grid for region1 */
+   AstPointSet *grid2;            /* PointSet holding grid for region2 */
+   AstPointSet *mesh1;            /* PointSet holding mesh for region1 */
+   AstPointSet *mesh2;            /* PointSet holding mesh for region2 */
+   AstPointSet *result;           /* Returned pointer */
+   AstPrism *this;                /* The Prism structure */
+   AstRegion *reg1;               /* Pointer to first component Region */
+   AstRegion *reg2;               /* Pointer to second component Region */
+   double **pg1;                  /* Pointer to grid1 arrays */
+   double **pg2;                  /* Pointer to grid2 arrays */
+   double **pm1;                  /* Pointer to mesh1 arrays */
+   double **pm2;                  /* Pointer to mesh2 arrays */
+   double **ptr;                  /* Pointer to returned mesh arrays */
+   int gsz1;                      /* Preferred grid size for region1 */
+   int gsz2;                      /* Preferred grid size for region2 */
+   int hasMesh1;                  /* Does 1st component Region have a mesh? */
+   int hasMesh2;                  /* Does 2nd component Region have a mesh? */
+   int i;                         /* Index of next mesh position */
+   int ii;                        /* Index of next results position */
+   int j;                         /* Index of next grid position */
+   int jc;                        /* Axis index */
+   int msz1;                      /* Preferred mesh size for region1 */
+   int msz2;                      /* Preferred mesh size for region2 */
+   int msz;                       /* Original MeshSize */
+   int mszp;                      /* MeshSize value for Prism */
+   int nax1;                      /* Number of axes in region1 */
+   int nax2;                      /* Number of axes in region2 */
+   int nax;                       /* Number of axes in Prism */
+
+/* Initialise */
+   result= NULL;
+
+/* Check the global error status. */
+   if ( !astOK ) return result;
+
+/* Get a pointer to the Prism structure. */
+   this = (AstPrism *) this_region;
+
+/* If the Region structure contains a pointer to a PointSet holding
+   a previously created mesh, return it. */
+   if( this_region->basemesh ) {
+      result = astClone( this_region->basemesh );
+
+/* Otherwise, create a new mesh. */
+   } else {
+
+/* Get pointers to the component regions. */
+      reg1 = this->region1;
+      reg2 = this->region2;
+
+/* A mesh can only be produced for a Region if it is bounded when either
+   negated or un-negated. See if meshes can be produced for the component
+   Regions. */
+      hasMesh1 = astGetBounded( reg1 );
+      if( !hasMesh1 ){
+         astNegate( reg1 );
+         hasMesh1 = astGetBounded( reg1 );
+         astNegate( reg1 );
+      }
+
+      hasMesh2 = astGetBounded( reg2 );
+      if( !hasMesh2 ){
+         astNegate( reg2 );
+         hasMesh2 = astGetBounded( reg2 );
+         astNegate( reg2 );
+      }
+
+/* If either Region does not have a mesh we cannot produce a mesh for the
+   Prism. */
+      if( !hasMesh1 || !hasMesh2 ) {
+         if( astOK ) astError( AST__INTER, "astRegBaseMesh(%s): No mesh "
+                   "can be produced for the %s bacause one of its component "
+                   "Regions is unbounded.", status, astGetClass( this ), astGetClass( this ) );
+
+/* Otherwise we can create a mesh for the Prism. */
+      } else {
+
+/* Determine the grid sizes and mesh sizes to use for the two components.
+   This aims to produce a total number of points in the returned Prism
+   mesh roughly equal to the MeshSize attribute of the Prism. It also
+   aims to divide the mesh points equally between the end faces of the
+   prism, and the side walls. We remember that the grid used to represent
+   any 1-D region always has a size of 2, regardless of the setting of
+   MeshSize. */
+         mszp = astGetMeshSize( this );
+         msz1 = ( astGetNaxes( reg1 ) == 1 ) ? 2 : sqrt( 0.5*mszp );
+         gsz2 = 0.5*mszp/msz1;
+         msz2 = ( astGetNaxes( reg2 ) == 1 ) ? 2 : sqrt( 0.5*mszp );
+         gsz1 = 0.5*mszp/msz2;
+
+/* First, get a boundary mesh for the second component Region defining the
+   prism extrusion. For instance, if the Region is 1-dimensional, this mesh
+   will consist of the two values on the Region axis: the lower and upper
+   bounds of the Region. */
+         msz = astTestMeshSize( reg2 ) ? astGetMeshSize( reg2 ) : -1;
+         astSetMeshSize( reg2, msz2 );
+         mesh2 = astRegMesh( reg2 );
+
+/* Also get a grid of points spread throughout the extent (i.e. not
+   merely on the boundary) of the second Region. */
+         astSetMeshSize( reg2, gsz2 );
+         grid2 = astRegGrid( reg2 );
+
+/* Re-instate the original MeshSize for the second Region. */
+         if( msz == -1 ) {
+            astClearMeshSize( reg2 );
+         } else {
+            astSetMeshSize( reg2, msz );
+         }
+
+/* Similarly, get a boundary mesh and a volume grid for the first Region. */
+         msz = astTestMeshSize( reg1 ) ? astGetMeshSize( reg1 ) : -1;
+         astSetMeshSize( reg1, msz1 );
+         mesh1 = astRegMesh( reg1 );
+
+         astSetMeshSize( reg1, gsz1 );
+         grid1 = astRegGrid( reg1 );
+
+         if( msz == -1 ) {
+            astClearMeshSize( reg1 );
+         } else {
+            astSetMeshSize( reg1, msz );
+         }
+
+/* Note the number of axes in the two component Regions. */
+         nax1 = astGetNcoord( mesh1 );
+         nax2 = astGetNcoord( mesh2 );
+
+/* The above mesh and grid sizes are only approximate. Find the values
+   actually used. */
+         msz1 = astGetNpoint( mesh1 );
+         gsz1 = astGetNpoint( grid1 );
+         msz2 = astGetNpoint( mesh2 );
+         gsz2 = astGetNpoint( grid2 );
+
+/* Create the returned PointSet. */
+         msz = gsz1*msz2 + msz1*gsz2;
+         nax= astGetNaxes( this );
+         result = astPointSet( msz, nax, "", status );
+
+/* Get pointers to the data in all 5 PointSets. */
+         ptr = astGetPoints( result );
+         pm1 = astGetPoints( mesh1 );
+         pg1 = astGetPoints( grid1 );
+         pm2 = astGetPoints( mesh2 );
+         pg2 = astGetPoints( grid2 );
+
+/* Check pointers can be de-referenced safely. */
+         if( astOK ) {
+
+/* Initialise the index of the next point to be written to the results
+   array. */
+            ii = 0;
+
+/* First, replicate the volume grid covering the first region at every
+   point in the boundary mesh covering the second Region. */
+            for( i = 0; i < msz2; i++ ) {
+               for( j = 0; j < gsz1; j++, ii++ ) {
+                  for( jc = 0; jc < nax1; jc++ ) {
+                     ptr[ jc ][ ii ] = pg1[ jc ][ j ];
+                  }
+                  for( ; jc < nax; jc++ ) {
+                     ptr[ jc ][ ii ] = pm2[ jc - nax1 ][ i ];
+                  }
+               }
+            }
+
+/* Now, replicate the volume grid covering the second region at every
+   point in the boundary mesh covering the first Region. */
+            for( i = 0; i < msz1; i++ ) {
+               for( j = 0; j < gsz2; j++, ii++ ) {
+                  for( jc = 0; jc < nax1; jc++ ) {
+                     ptr[ jc ][ ii ] = pm1[ jc ][ i ];
+                  }
+                  for( ; jc < nax; jc++ ) {
+                     ptr[ jc ][ ii ] = pg2[ jc -nax1 ][ j ];
+                  }
+               }
+            }
+         }
+
+/* Free resources. */
+         mesh1 = astAnnul( mesh1 );
+         mesh2 = astAnnul( mesh2 );
+         grid1 = astAnnul( grid1 );
+         grid2 = astAnnul( grid2 );
+      }
+
+/* Save the returned pointer in the Region structure so that it does not
+   need to be created again next time this function is called. */
+      if( astOK && result ) this_region->basemesh = astClone( result );
+   }
+
+/* Annul the result if an error has occurred. */
+   if( !astOK ) result = astAnnul( result );
+
+/* Return a pointer to the output PointSet. */
+   return result;
+}
+
+static AstRegion *RegBasePick( AstRegion *this_region, int naxes,
+                               const int *axes, int *status ){
+/*
+*  Name:
+*     RegBasePick
+
+*  Purpose:
+*     Return a Region formed by picking selected base Frame axes from the
+*     supplied Region.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     AstRegion *RegBasePick( AstRegion *this, int naxes, const int *axes,
+*                             int *status )
+
+*  Class Membership:
+*     Prism member function (over-rides the astRegBasePick protected
+*     method inherited from the Region class).
+
+*  Description:
+*     This function attempts to return a Region that is spanned by selected
+*     axes from the base Frame of the encapsulated FrameSet of the supplied
+*     Region. This may or may not be possible, depending on the class of
+*     Region. If it is not possible a NULL pointer is returned.
+
+*  Parameters:
+*     this
+*        Pointer to the Region.
+*     naxes
+*        The number of base Frame axes to select.
+*     axes
+*        An array holding the zero-based indices of the base Frame axes
+*        that are to be selected.
+*     status
+*        Pointer to the inherited status variable.
+
+*  Returned Value:
+*     Pointer to the Region, or NULL if no region can be formed.
+
+*  Notes:
+*    - A NULL pointer is returned if an error has already occurred, or if
+*    this function should fail for any reason.
+*/
+
+/* Local Variables: */
+   AstFrame *frm1;      /* Axes picked from the 1st encapsulated Region */
+   AstFrame *frm2;      /* Axes picked from the 2nd encapsulated Region */
+   AstPrism *this;      /* Pointer to Prism structure */
+   AstRegion *result;   /* Returned Region */
+   int *axes1;          /* Axes to pick from 1st input encapsulated Region */
+   int *axes2;          /* Axes to pick from 2nd input encapsulated Region */
+   int i;               /* Output axis index */
+   int j;               /* Input axis index */
+   int nax1;            /* No. of axes in 1st input encapsulated Region */
+   int nax2;            /* No. of axes in 2nd input encapsulated Region */
+   int naxes1;          /* No. of axes in 1st output encapsulated Region */
+   int naxes2;          /* No. of axes in 2nd output encapsulated Region */
+
+/* Initialise */
+   result = NULL;
+
+/* Check the global error status. */
+   if ( !astOK ) return result;
+
+/* Get a pointer to the Prism information. */
+   this = (AstPrism *) this_region;
+
+/* Get the number of axes in each of the two encapsulated Regions. */
+   nax1 = astGetNaxes( this->region1 );
+   nax2 = astGetNaxes( this->region2 );
+
+/* Allocate memory to hold the indices of the axes selected from each of
+   the two encapsulated Regions. */
+   axes1 = astMalloc( sizeof( *axes1 )*nax1 );
+   axes2 = astMalloc( sizeof( *axes2 )*nax2 );
+
+/* Check pointers can be used safely. */
+   if( astOK ) {
+
+/* Initialise the counters that count the number of axes selected from
+   each of the two encapsulated Regions. */
+      naxes1 = 0;
+      naxes2 = 0;
+
+/* For each of the axes to be selected from the prism... */
+      for( i = 0; i < naxes; i++ ) {
+         j = axes[ i ];
+
+/* ... if the current selected axis is part of the first encapsulated
+   Region, add its index into the array that holds the axes to be selected
+   from the first encapsulated region. Increment the number of axes
+   selected from the first encapsulated region. */
+         if( j < nax1 ) {
+            axes1[ naxes1++ ] = j;
+
+/* If the current selected axis is part of the second encapsulated Region,
+   add its index into the array that holds the axes to be selected from
+   the second encapsulated region. Note, the index is converted from a
+   Prism axis index to a sub-region axis index by subtracting "nax1".
+   Also increment the number of axes selected from the second encapsulated
+   region. */
+         } else {
+            axes2[ naxes2++ ] = j - nax1;
+         }
+      }
+
+/* Pick any required axes from the first sub-region. If the result of the
+   selection is not a Region, we cannot pick the required axes, so annul
+   the object holding the selected axes. */
+      if( naxes1 ) {
+         frm1 = astPickAxes( this->region1, naxes1, axes1, NULL );
+         if( frm1 && !astIsARegion( frm1 ) ) frm1 = astAnnul( frm1 );
+      } else {
+         frm1 = NULL;
+      }
+
+/* Pick any required axes from the second sub-region. If the result of the
+   selection is not a Region, we cannot pick the required axes, so annul
+   the object holding the selected axes. */
+      if( naxes2 ) {
+         frm2 = astPickAxes( this->region2, naxes2, axes2, NULL );
+         if( frm2 && !astIsARegion( frm2 ) ) frm2 = astAnnul( frm2 );
+      } else {
+         frm2 = NULL;
+      }
+
+/* If we are selecting axes only from the first sub-region, and the above
+   selection was succesful, just return a clone of the Region holding the
+   axes selected from the first sub-region. */
+      if( naxes1 > 0 && naxes2 == 0 && frm1 ) {
+         result = astClone( frm1 );
+
+/* If we are selecting axes only from the second sub-region, and the above
+   selection was succesful, just return a clone of the Region holding the
+   axes selected from the second sub-region. */
+      } else if( naxes1 == 0 && naxes2 > 0 && frm2 ) {
+         result = astClone( frm2 );
+
+/* If we are selecting axes from both sub-regions, and both the above
+   selections were succesful, joing them together into a Prism. */
+      } else if( naxes1 > 0 && naxes2 > 0 && frm1 && frm2 ) {
+         result = (AstRegion *) astPrism( (AstRegion *) frm1,
+                                          (AstRegion *) frm2,
+                                          "", status );
+      }
+
+/* Free resources */
+      if( frm1 ) frm1 = astAnnul( frm1 );
+      if( frm2 ) frm2 = astAnnul( frm2 );
+   }
+
+   axes1 = astFree( axes1 );
+   axes2 = astFree( axes2 );
+
+/* Return a NULL pointer if an error has occurred. */
+   if( !astOK ) result = astAnnul( result );
+
+/* Return the result. */
+   return result;
+}
+
+static double *RegCentre( AstRegion *this_region, double *cen, double **ptr,
+                          int index, int ifrm, int *status ){
+/*
+*  Name:
+*     RegCentre
+
+*  Purpose:
+*     Re-centre a Region.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     double *RegCentre( AstRegion *this, double *cen, double **ptr,
+*                        int index, int ifrm, int *status )
+
+*  Class Membership:
+*     Prism member function (over-rides the astRegCentre protected
+*     method inherited from the Region class).
+
+*  Description:
+*     This function shifts the centre of the supplied Region to a
+*     specified position, or returns the current centre of the Region.
+
+*  Parameters:
+*     this
+*        Pointer to the Region.
+*     cen
+*        Pointer to an array of axis values, giving the new centre.
+*        Supply a NULL value for this in order to use "ptr" and "index" to
+*        specify the new centre.
+*     ptr
+*        Pointer to an array of points, one for each axis in the Region.
+*        Each pointer locates an array of axis values. This is the format
+*        returned by the PointSet method astGetPoints. Only used if "cen"
+*        is NULL.
+*     index
+*        The index of the point within the arrays identified by "ptr" at
+*        which is stored the coords for the new centre position. Only used
+*        if "cen" is NULL.
+*     ifrm
+*        Should be AST__BASE or AST__CURRENT. Indicates whether the centre
+*        position is supplied and returned in the base or current Frame of
+*        the FrameSet encapsulated within "this".
+*     status
+*        Pointer to the inherited status variable.
+
+*  Returned Value:
+*     If both "cen" and "ptr" are NULL then a pointer to a newly
+*     allocated dynamic array is returned which contains the centre
+*     coords of the Region. This array should be freed using astFree when
+*     no longer needed. If either of "ptr" or "cen" is not NULL, then a
+*     NULL pointer is returned.
+
+*  Notes:
+*    - Some Region sub-classes do not have a centre. Such classes will report
+*    an AST__INTER error code if this method is called with either "ptr" or
+*    "cen" not NULL. If "ptr" and "cen" are both NULL, then no error is
+*    reported if this method is invoked on a Region of an unsuitable class,
+*    but NULL is always returned.
+*/
+
+/* Local Variables: */
+   AstPrism *this;     /* Pointer to Prism structure */
+   AstRegion *reg1;    /* Pointer to first component Region */
+   AstRegion *reg2;    /* Pointer to second component Region */
+   double *bc;         /* Base Frame centre position */
+   double *cen1;       /* Centre of first component Region */
+   double *cen2;       /* Centre of second component Region */
+   double *result;     /* Returned pointer */
+   double *tmp;        /* Temporary array pointer */
+   double *total;      /* Pointer to total base Frame centre array */
+   int i;              /* Coordinate index */
+   int nax1;           /* Number of axes in first component Region */
+   int nax2;           /* Number of axes in second component Region */
+   int ncb;            /* Number of base frame coordinate values per point */
+   int ncc;            /* Number of current frame coordinate values per point */
+   int neg;            /* Prism negated flag */
+
+/* Initialise */
+   result = NULL;
+
+/* Check the local error status. */
+   if ( !astOK ) return result;
+
+/* Get a pointer to the Prism structure. */
+   this = (AstPrism *) this_region;
+
+/* Get the component Regions, and the Negated flag for the Prism. */
+   GetRegions( this, &reg1, &reg2, &neg, status );
+
+/* Get the number of current Frame axes in each component Region. The sum
+   of these will equal the number of base Frame axes in the parent Region
+   structure. */
+   nax1 = astGetNaxes( reg1 );
+   nax2 = astGetNaxes( reg2 );
+   ncb = nax1 + nax2;
+
+/* If we are getting (not setting) the current centre... */
+   if( !ptr && !cen ) {
+
+/* Get the centre from the two component Regions in their current Frames. */
+      cen1 = astRegCentre( reg1, NULL, NULL, 0, AST__CURRENT );
+      cen2 = astRegCentre( reg2, NULL, NULL, 0, AST__CURRENT );
+
+/* If both component regions are re-centerable, join the two centre
+   arrays together into a single array. */
+      if( cen1 && cen2 ) {
+         total = astMalloc( sizeof(double)*(size_t)ncb );
+         if( total ) {
+            for( i = 0; i < nax1; i++ ) total[ i ] = cen1[ i ];
+            for( i = 0; i < nax2; i++ ) total[ i + nax1 ] = cen2[ i ];
+
+/* The current Frames of the component Regions correspond to the base
+   Frame of the parent Region structure. If the original centre is
+   required in the current Frame, transform it using the base->current
+   Mapping from the parent Region structure. */
+            if( ifrm == AST__CURRENT ) {
+               result = astRegTranPoint( this_region, total, 1, 1 );
+               total = astFree( total );
+            } else {
+               result = total;
+            }
+         }
+      }
+
+/* Free the individual centre arrays. */
+      cen1 = astFree( cen1 );
+      cen2 = astFree( cen2 );
+
+/* If we are setting a new centre... */
+   } else {
+
+/* If the new centre is supplied in the current Frame of the parent
+   Region structure, transform it into the base Frame (i.e. the Frames
+   represented by the component Regions). */
+      if( ifrm == AST__CURRENT ) {
+         if( cen ) {
+            bc = astRegTranPoint( this_region, cen, 1, 0 );
+         } else {
+            ncc = astGetNaxes( this_region );
+            tmp = astMalloc( sizeof( double)*(size_t)ncc );
+            if( astOK ) {
+               for( i = 0; i < ncc; i++ ) tmp[ i ] = ptr[ i ][ index ];
+            }
+            bc = astRegTranPoint( this_region, tmp, 1, 0 );
+            tmp = astFree( tmp );
+         }
+
+      } else {
+         if( cen ) {
+            bc = cen;
+         } else {
+            bc = astMalloc( sizeof( double)*(size_t)ncb );
+            if( astOK ) {
+               for( i = 0; i < ncb; i++ ) bc[ i ] = ptr[ i ][ index ];
+            }
+         }
+      }
+
+/* Set the centre in the two component Regions in their current Frames. */
+      astRegCentre( reg1, bc, NULL, 0, AST__CURRENT );
+      astRegCentre( reg2, bc + nax1, NULL, 0, AST__CURRENT );
+
+/* Free resources. */
+     if( bc != cen ) bc = astFree( bc );
+   }
+
+   reg1 = astAnnul( reg1 );
+   reg2 = astAnnul( reg2 );
+
+/* Return the result. */
+   return result;
+}
+
+static int RegPins( AstRegion *this_region, AstPointSet *pset, AstRegion *unc,
+                    int **mask, int *status ){
+/*
+*  Name:
+*     RegPins
+
+*  Purpose:
+*     Check if a set of points fall on the boundary of a given Prism.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     int RegPins( AstRegion *this, AstPointSet *pset, AstRegion *unc,
+*                  int **mask, int *status )
+
+*  Class Membership:
+*     Prism member function (over-rides the astRegPins protected
+*     method inherited from the Region class).
+
+*  Description:
+*     This function returns a flag indicating if the supplied set of
+*     points all fall on the boundary of the given Prism.
+*
+*     Some tolerance is allowed, as specified by the uncertainty Region
+*     stored in the supplied Prism "this", and the supplied uncertainty
+*     Region "unc" which describes the uncertainty of the supplied points.
+
+*  Parameters:
+*     this
+*        Pointer to the Prism.
+*     pset
+*        Pointer to the PointSet. The points are assumed to refer to the
+*        base Frame of the FrameSet encapsulated by "this".
+*     unc
+*        Pointer to a Region representing the uncertainties in the points
+*        given by "pset". The Region is assumed to represent the base Frame
+*        of the FrameSet encapsulated by "this". Zero uncertainity is assumed
+*        if NULL is supplied.
+*     mask
+*        Pointer to location at which to return a pointer to a newly
+*        allocated dynamic array of ints. The number of elements in this
+*        array is equal to the value of the Npoint attribute of "pset".
+*        Each element in the returned array is set to 1 if the
+*        corresponding position in "pset" is on the boundary of the Region
+*        and is set to zero otherwise. A NULL value may be supplied
+*        in which case no array is created. If created, the array should
+*        be freed using astFree when no longer needed.
+*     status
+*        Pointer to the inherited status variable.
+
+*  Returned Value:
+*     Non-zero if the points all fall on the boundary of the given
+*     Region, to within the tolerance specified. Zero otherwise.
+
+*/
+
+/* Local variables: */
+   AstPointSet *ps1;            /* Points projected into 1st component Region */
+   AstPointSet *ps1b;           /* "ps1" in base Frame of 1st component Region */
+   AstPointSet *ps1b2;          /* "ps1b" transformed using 1st Region */
+   AstPointSet *ps2b2;          /* "ps2b" transformed using 2nd Region */
+   AstPointSet *ps2;            /* Points projected into 2nd component Region */
+   AstPointSet *ps2b;           /* "ps2" in base Frame of 2nd component Region */
+   AstPrism *this;              /* Pointer to the Prism structure. */
+   AstRegion *reg1;             /* Pointer to first component Region */
+   AstRegion *reg2;             /* Pointer to second component Region */
+   AstRegion *unc1;             /* Base Frame uncertainty in 1st component Region */
+   AstRegion *unc2;             /* Base Frame uncertainty in 2nd component Region */
+   double **ptr1b2;             /* Pointer to axis values in "ps1b2" */
+   double **ptr2b2;             /* Pointer to axis values in "ps2b2" */
+   int *mask1;                  /* Mask for first component boundary */
+   int *mask2;                  /* Mask for second component boundary */
+   int cl1;                     /* Original Closed flag for reg1 */
+   int cl2;                     /* Original Closed flag for reg2 */
+   int i;                       /* Point index */
+   int j;                       /* Axis index */
+   int nax1;                    /* Number of axes in first component Region */
+   int nax2;                    /* Number of axes in second component Region */
+   int np;                      /* Number of points in supplied PointSet */
+   int on;                      /* Is this point on the Prism boundary? */
+   int result;                  /* Returned flag */
+
+/* Initialise */
+   result = 0;
+   if( mask ) *mask = NULL;
+
+/* Check the inherited status. */
+   if( !astOK ) return result;
+
+/* Get a pointer to the Prism structure. */
+   this = (AstPrism *) this_region;
+
+/* Get pointers to the two component Regions. */
+   reg1 = this->region1;
+   reg2 = this->region2;
+
+/* Temporarily ensure the components are closed. */
+   cl1 = astTestClosed( reg1 ) ? astGetClosed( reg1 ) : INT_MAX;
+   cl2 = astTestClosed( reg2 ) ? astGetClosed( reg2 ) : INT_MAX;
+   astSetClosed( reg1, cl1 );
+   astSetClosed( reg2, cl2 );
+
+/* A point in the coordinate system represented by the Prism is on the
+   boundary of the Prism if:
+   1) it is on the boundary of one of the coomponent Regions AND
+   2) it is on or within the boundary of the other component Region.
+
+   First look for points on the boundary of the first component Region.
+   Create a PointSet holding just the axes from the supplied PointSet
+   which relate to the first component Region. */
+   np = astGetNpoint( pset );
+   nax1 = astGetNaxes( reg1 );
+   ps1 = astPointSet( np, nax1, "", status );
+   astSetSubPoints( pset, 0, 0, ps1 );
+
+/* Get a mask which indicates if each supplied point is on or off the
+   boundary of the first component Region. astRegPins expects its "pset"
+   argument to contain positions in the base Frame of the Region, so
+   we must first transform the supplied points into the base Frame of
+   "reg1". We must also get the uncertainty in the base Frame of the
+   component Region. */
+   ps1b = astRegTransform( reg1, ps1, 0, NULL, NULL );
+   unc1 = astGetUncFrm( reg1, AST__BASE );
+   astRegPins( reg1, ps1b, unc1, &mask1 );
+
+/* Also determine which of the points are on or in the boundary by using
+   "reg1" as a Mapping to transform the supplied points. */
+   ps1b2 = astTransform( reg1, ps1b, 1, NULL );
+
+/* Do the same for the second component Region */
+   nax2 = astGetNaxes( reg2 );
+   ps2 = astPointSet( np, nax2, "", status );
+   astSetSubPoints( pset, 0, nax1, ps2 );
+   ps2b = astRegTransform( reg2, ps2, 0, NULL, NULL );
+   unc2 = astGetUncFrm( reg2, AST__BASE );
+   astRegPins( reg2, ps2b, unc2, &mask2 );
+   ps2b2 = astTransform( reg2, ps2b, 1, NULL );
+
+/* Get pointers to the data in all the relevant PointSets. */
+   ptr1b2 = astGetPoints( ps1b2 );
+   ptr2b2 = astGetPoints( ps2b2 );
+
+/* Check pointers can be dereferenced safely. */
+   if( astOK ) {
+
+/* Assume all points are on the boundary of the Prism. */
+      result = 1;
+
+/* Check each point. */
+      for( i = 0; i < np; i++ ) {
+
+/* Assume this point is on the boundary of the Prism. */
+         on = 1;
+
+/* If this point is on the boundary of both component Regions, it is on
+   the boundary of the Prism. If it is on the boundary of the first
+   component Region but not on the boundary of the second, then it is
+   still on the boundary of the Prism if it is within the volume
+   reporesented by the second. */
+         if( mask1[ i ] ) {
+            if( !mask2[ i ] ) {
+               for( j = 0; j < nax2; j++ ) {
+                  if( ptr2b2[ j ][ i ] == AST__BAD ) {
+                     on = 0;
+                     break;
+                  }
+               }
+            }
+
+/* If this point is on the boundary of the second component Region but
+   not the first, it is on the boundary of the Prism if it is within the
+   volume reporesented by the first. */
+         } else {
+            if( mask2[ i ] ) {
+               for( j = 0; j < nax1; j++ ) {
+                  if( ptr1b2[ j ][ i ] == AST__BAD ) {
+                     on = 0;
+                     break;
+                  }
+               }
+
+/* If this point is on the boundary of neither component Region, it is not
+   on the boundary of the Prism. */
+            } else {
+               on = 0;
+            }
+         }
+
+/* Use "mask1" to return the Prism's mask. Clear the returned flag if
+   this point is not on the boundary of the Prism. */
+         mask1[ i ] = on;
+         if( !on ) result = 0;
+      }
+   }
+
+/* Re-instate the original values of the Closed attribute for the
+   component Regions. */
+   if( cl1 == INT_MAX ) {
+      astClearClosed( reg1 );
+   } else {
+      astSetClosed( reg1, cl1 );
+   }
+   if( cl2 == INT_MAX ) {
+      astClearClosed( reg2 );
+   } else {
+      astSetClosed( reg2, cl2 );
+   }
+
+/* Return "mask1" as the Prism's mask if required. Otherwise free it. */
+   if( mask ) {
+      *mask = mask1;
+   } else {
+      mask1 = astFree( mask1 );
+   }
+
+/* Free other resources */
+   mask2 = astFree( mask2 );
+   ps1 = astAnnul( ps1 );
+   ps1b = astAnnul( ps1b );
+   ps1b2 = astAnnul( ps1b2 );
+   ps2 = astAnnul( ps2 );
+   unc1 = astAnnul( unc1 );
+   ps2b = astAnnul( ps2b );
+   ps2b2 = astAnnul( ps2b2 );
+   unc2 = astAnnul( unc2 );
+
+/* If an error has occurred, return zero. */
+   if( !astOK ) {
+      result = 0;
+      if( mask ) *mask = astFree( *mask );
+   }
+
+/* Return the result. */
+   return result;
+}
+
+static void RegClearAttrib( AstRegion *this_region, const char *attrib,
+                            char **base_attrib, int *status ) {
+/*
+*  Name:
+*     RegClearAttrib
+
+*  Purpose:
+*     Clear an attribute value for a Region.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     void RegClearAttrib( AstRegion *this, const char *attrib,
+*                          char **base_attrib, int *status )
+
+*  Class Membership:
+*     Prism member function (over-rides the astRegClearAttrib method
+*     inherited from the Region class).
+
+*  Description:
+*     This function clears the value of a named attribute in both the base
+*     and current Frame in the FrameSet encapsulated within a Region, without
+*     remapping either Frame.
+*
+*     No error is reported if the attribute is not recognised by the base
+*     Frame.
+
+*  Parameters:
+*     this
+*        Pointer to the Region.
+*     attrib
+*        Pointer to a null terminated string holding the attribute name.
+*        NOTE, IT SHOULD BE ENTIRELY LOWER CASE.
+*     base_attrib
+*        Address of a location at which to return a pointer to the null
+*        terminated string holding the attribute name which was cleared in
+*        the base Frame of the encapsulated FrameSet. This may differ from
+*        the supplied attribute if the supplied attribute contains an axis
+*        index and the current->base Mapping in the FrameSet produces an
+*        axis permutation. The returned pointer should be freed using
+*        astFree when no longer needed. A NULL pointer may be supplied in
+*        which case no pointer is returned.
+*     status
+*        Pointer to the inherited status variable.
+
+*/
+
+/* Local Variables: */
+   AstPrism *this;
+   AstRegion *creg;
+   char *batt;
+   char buf1[ 100 ];
+   char buf2[ 255 ];
+   int axis;
+   int len;
+   int nax1;
+   int nc;
+   int rep;
+
+/* Check the global error status. */
+   if ( !astOK ) return;
+
+/* Get a pointer to the Prism structure. */
+   this = (AstPrism *) this_region;
+
+/* Use the RegClearAttrib method inherited from the parent class to clear the
+   attribute in the current and base Frames in the FrameSet encapsulated by
+   the parent Region structure. */
+   (*parent_regclearattrib)( this_region, attrib, &batt, status );
+
+/* We now propagate the setting down to the component Regions. The current
+   Frames in the component Regions together form a CmpFrame which is
+   equivalent to the base Frame in the parent FrameSet. Switch off error
+   reporting whilst we apply the setting to the component Regions. */
+   rep = astReporting( 0 );
+
+/* If the setting which was applied to the base Frame of the parent FrameSet
+   is qualified by an axis index, modify the axis index to refer to component
+   Region which defines the axis. First parse the base Frame attribute setting
+   to locate any axis index. */
+   len = strlen( batt );
+   if( nc = 0, ( 2 == astSscanf( batt, "%[^(](%d) %n", buf1, &axis,
+                                 &nc ) ) && ( nc >= len ) ) {
+
+/* If found, convert the axis index from one-based to zero-based. */
+      axis--;
+
+/* Get a pointer to the component Region containing the specified axis, and
+   create a new setting with the same attribute name but with the axis index
+   appropriate to the component Region which defines the axis. */
+      nax1 = astGetNaxes( this->region1 );
+      if( axis < nax1 ) {
+         creg = this->region1;
+      } else {
+         creg = this->region2;
+         axis -= nax1;
+      }
+      sprintf( buf2, "%s(%d)", buf1, axis + 1 );
+
+/* Apply the setting to the relevant component Region. */
+      astRegClearAttrib( creg, buf2, NULL );
+
+/* If the setting is not qualified by an axis index, apply it to both
+   component Regions. */
+   } else {
+      astRegClearAttrib( this->region1, batt, NULL );
+      astRegClearAttrib( this->region2, batt, NULL );
+   }
+
+/* Annul the error if the attribute was not recognised by the component
+   Regions. Then switch error reporting back on. */
+   if( astStatus == AST__BADAT ) astClearStatus;
+   astReporting( rep );
+
+/* If required, return the base Frame setting string. Otherwise free it. */
+   if( base_attrib ) {
+      *base_attrib = batt;
+   } else {
+      batt = astFree( batt );
+   }
+
+}
+
+static void RegSetAttrib( AstRegion *this_region, const char *setting,
+                          char **base_setting, int *status ) {
+/*
+*  Name:
+*     RegSetAttrib
+
+*  Purpose:
+*     Set an attribute value for a Region.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     void RegSetAttrib( AstRegion *this, const char *setting,
+*                        char **base_setting, int *status )
+
+*  Class Membership:
+*     Prism method (over-rides the astRegSetAttrib method inherited from
+*     the Region class).
+
+*  Description:
+*     This function assigns an attribute value to both the base and
+*     current Frame in the FrameSet encapsulated within a Region, without
+*     remapping either Frame.
+*
+*     No error is reported if the attribute is not recognised by the base
+*     Frame.
+
+*  Parameters:
+*     this
+*        Pointer to the Region.
+*     setting
+*        Pointer to a null terminated attribute setting string. NOTE, IT
+*        SHOULD BE ENTIRELY LOWER CASE. The supplied string will be
+*        interpreted using the public interpretation implemented by
+*        astSetAttrib. This can be different to the interpretation of the
+*        protected accessor functions. For instance, the public
+*        interpretation of an unqualified floating point value for the
+*        Epoch attribute is to interpet the value as a gregorian year,
+*        but the protected interpretation is to interpret the value as an
+*        MJD.
+*     base_setting
+*        Address of a location at which to return a pointer to the null
+*        terminated attribute setting string which was applied to the
+*        base Frame of the encapsulated FrameSet. This may differ from
+*        the supplied setting if the supplied setting contains an axis
+*        index and the current->base Mapping in the FrameSet produces an
+*        axis permutation. The returned pointer should be freed using
+*        astFree when no longer needed. A NULL pointer may be supplied in
+*        which case no pointer is returned.
+*     status
+*        Pointer to the inherited status variable.
+
+*/
+
+/* Local Variables: */
+   AstPrism *this;
+   AstRegion *creg;
+   char *bset;
+   char buf1[ 100 ];
+   char buf2[ 255 ];
+   int axis;
+   int len;
+   int nax1;
+   int nc;
+   int rep;
+   int value;
+
+/* Check the global error status. */
+   if ( !astOK ) return;
+
+/* Get a pointer to the Prism structure. */
+   this = (AstPrism *) this_region;
+
+/* Use the RegSetAttrib method inherited from the parent class to apply the
+   setting to the current and base Frames in the FrameSet encapsulated by the
+   parent Region structure. */
+   (*parent_regsetattrib)( this_region, setting, &bset, status );
+
+/* We now propagate the setting down to the component Regions. The current
+   Frames in the component Regions together form a CmpFrame which is
+   equivalent to the base Frame in the parent FrameSet. Switch off error
+   reporting whilst we apply the setting to the component Regions. */
+   rep = astReporting( 0 );
+
+/* If the setting which was applied to the base Frame of the parent FrameSet
+   is qualified by an axis index, modify the axis index to refer to component
+   Region which defines the axis. First parse the base Frame attribute setting
+   to locate any axis index. */
+   len = strlen( bset );
+   if( nc = 0, ( 2 == astSscanf( bset, "%[^(](%d)= %n%*s %n", buf1, &axis,
+                                 &value, &nc ) ) && ( nc >= len ) ) {
+
+/* If found, convert the axis index from one-based to zero-based. */
+      axis--;
+
+/* Get a pointer to the component Region containing the specified axis, and
+   create a new setting with the same attribute name but with the axis index
+   appropriate to the component Region which defines the axis. */
+      nax1 = astGetNaxes( this->region1 );
+      if( axis < nax1 ) {
+         creg = this->region1;
+      } else {
+         creg = this->region2;
+         axis -= nax1;
+      }
+      sprintf( buf2, "%s(%d)=%s", buf1, axis + 1, bset + value );
+
+/* Apply the setting to the relevant component Region. */
+      astRegSetAttrib( creg, buf2, NULL );
+
+/* If the setting is not qualified by an axis index, apply it to both
+   component Regions. */
+   } else {
+      astRegSetAttrib( this->region1, bset, NULL );
+      astRegSetAttrib( this->region2, bset, NULL );
+   }
+
+/* Annul the error if the attribute was not recognised by the component
+   Regions. Then switch error reporting back on. */
+   if( astStatus == AST__BADAT ) astClearStatus;
+   astReporting( rep );
+
+/* If required, return the base Frame setting string. Otherwise free it. */
+   if( base_setting ) {
+      *base_setting = bset;
+   } else {
+      bset = astFree( bset );
+   }
+
+}
+
+static void SetRegFS( AstRegion *this_region, AstFrame *frm, int *status ) {
+/*
+*  Name:
+*     SetRegFS
+
+*  Purpose:
+*     Stores a new FrameSet in a Region
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     void SetRegFS( AstRegion *this_region, AstFrame *frm, int *status )
+
+*  Class Membership:
+*     Prism method (over-rides the astSetRegFS method inherited from
+*     the Region class).
+
+*  Description:
+*     This function creates a new FrameSet and stores it in the supplied
+*     Region. The new FrameSet contains two copies of the supplied
+*     Frame, connected by a UnitMap.
+
+*  Parameters:
+*     this
+*        Pointer to the Region.
+*     frm
+*        The Frame to use.
+*     status
+*        Pointer to the inherited status variable.
+
+*/
+
+/* Local Variables: */
+   AstFrame *cfrm;         /* Frame containing required axes */
+   AstRegion *creg;        /* Pointer to component Region structure */
+   int *axes;              /* Pointer to array of axis indices */
+   int i;                  /* Loop count */
+   int nax1;               /* No.of axes in 1st component Frame */
+   int nax2;               /* No.of axes in 2nd component Frame */
+
+/* Check the global error status. */
+   if ( !astOK ) return;
+
+/* Invoke the parent method to store the FrameSet in the parent Region
+   structure. */
+   (* parent_setregfs)( this_region, frm, status );
+
+/* If either component Region has a dummy FrameSet use this method
+   recursively to give them a FrameSet containing the corresponding axes
+   from the supplied Frame. */
+   creg = ((AstPrism *) this_region )->region1;
+   if( creg ) {
+      nax1 = astGetNaxes( creg );
+      if( !astGetRegionFS( creg ) ) {
+         axes = astMalloc( sizeof( int )*(size_t) nax1 );
+         if( astOK ) for( i = 0; i < nax1; i++ ) axes[ i ] = i;
+         cfrm = astPickAxes( frm, nax1, axes, NULL );
+         astSetRegFS( creg, cfrm );
+         axes = astFree( axes );
+         cfrm = astAnnul( cfrm );
+      }
+
+   } else {
+      nax1 = 0;
+   }
+
+   creg = ((AstPrism *) this_region )->region2;
+   if( creg && !astGetRegionFS( creg ) ) {
+      nax2 = astGetNaxes( creg );
+      axes = astMalloc( sizeof( int )*(size_t) nax2 );
+      if( astOK ) for( i = 0; i < nax2; i++ ) axes[ i ] = nax1 + i;
+      cfrm = astPickAxes( frm, nax2, axes, NULL );
+      astSetRegFS( creg, cfrm );
+      axes = astFree( axes );
+      cfrm = astAnnul( cfrm );
+   }
+
+}
+
+static AstMapping *Simplify( AstMapping *this_mapping, int *status ) {
+/*
+*  Name:
+*     Simplify
+
+*  Purpose:
+*     Simplify a Region.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "region.h"
+*     AstMapping *Simplify( AstMapping *this, int *status )
+
+*  Class Membership:
+*     Prism method (over-rides the astSimplify method inherited from
+*     the Region class).
+
+*  Description:
+*     This function simplifies a Prism to eliminate redundant
+*     computational steps, or to merge separate steps which can be
+*     performed more efficiently in a single operation.
+
+*  Parameters:
+*     this
+*        Pointer to the original Region.
+*     status
+*        Pointer to the inherited status variable.
+
+*  Returned Value:
+*     A new pointer to the (possibly simplified) Region.
+
+*  Notes:
+*     - A NULL pointer value will be returned if this function is
+*     invoked with the AST error status set, or if it should fail for
+*     any reason.
+
+*  Deficiencies:
+*     - Currently, this function does not attempt to map the component
+*     Regions into the current Frame of the parent Region structure.
+
+*/
+
+/* Local Variables: */
+   AstFrame *cfrm;               /* Current Frame */
+   AstFrame *newfrm1;            /* Current Frame axes for reg1 */
+   AstFrame *newfrm2;            /* Current Frame axes for reg2 */
+   AstFrameSet *fs;              /* Parent FrameSet */
+   AstMapping *bcmap;            /* Base->current Mapping */
+   AstMapping *nmap1;            /* Reg1->current Mapping */
+   AstMapping *map1;             /* First component Region from a CmpMap */
+   AstMapping *map2;             /* Second component Region from a CmpMap */
+   int series;                   /* Apply component Mappings in series? */
+   int invert1;                  /* Use inverted first component Mapping? */
+   int invert2;                  /* Use inverted second component Mapping? */
+   AstMapping *nmap2;            /* Reg2->current Mapping */
+   AstMapping *result;           /* Result pointer to return */
+   AstCmpMap *cmpmap;            /* Result pointer to return */
+   AstMapping *smap;             /* Simplified CmpMap */
+   AstRegion *new2;              /* New simplified Region */
+   AstRegion *new;               /* New Region */
+   AstRegion *newreg1;           /* Reg1 mapped into current Frame */
+   AstRegion *newreg2;           /* Reg2 mapped into current Frame */
+   AstRegion *reg1;              /* First component Region */
+   AstRegion *reg2;              /* Second component Region */
+   AstRegion *reg;               /* This Region */
+   AstRegion *snewreg1;          /* Simplified newreg1 */
+   AstRegion *snewreg2;          /* Simplified newreg2 */
+   AstRegion *unc;               /* Uncertainty Region from supplied Prism */
+   int *axin;                    /* Indices of Mapping inputs to use */
+   int *axout1;                  /* Indices of cfrm axes corresponding to reg1 */
+   int *axout2;                  /* Indices of cfrm axes corresponding to reg2 */
+   int *perm;                    /* Axis permutation array */
+   int i;                        /* Loop count */
+   int nax1;                     /* Number of axes in first component Region */
+   int nax2;                     /* Number of axes in second component Region */
+   int naxt;                     /* Total number of axes in current Frame */
+   int naxout1;                  /* Number of current axes for reg1 */
+   int naxout2;                  /* Number of current axes for reg2 */
+   int neg;                      /* Negated flag for supplied Prism */
+
+/* Initialise. */
+   result = NULL;
+
+/* Check the global error status. */
+   if ( !astOK ) return result;
+
+/* Get a pointer to the Region structure */
+   reg = (AstRegion *) this_mapping;
+
+/* Get the component Regions, and the Negated flag for the Prism. */
+   GetRegions( (AstPrism *) this_mapping, &reg1, &reg2, &neg, status );
+
+/* The above Regions describe areas within the base Frame of the FrameSet
+   encapsulated by the parent Region structure. Get the current Frame in
+   this FrameSet and the base->current Mapping. */
+   fs = reg->frameset;
+   cfrm = astGetFrame( fs, AST__CURRENT );
+   bcmap = astGetMapping( fs, AST__BASE, AST__CURRENT );
+
+/* Combine the two Regions into a parallel CmpMap (this uses the fact
+   that a Region is a type of Mapping). Then simplify the CmpMap. This
+   will result in the astMapMerge methods defined by sub-classes of
+   Regions being used to merge adjacent regions. */
+   cmpmap = astCmpMap( reg1, reg2, 0, "", status );
+   smap = astSimplify( cmpmap );
+   cmpmap = astAnnul( cmpmap );
+
+/* Initially, assume we cannot form a new Region from the simplified
+   CmpMap. */
+   new = NULL;
+
+/* If the result is a region, use it. */
+   if( astIsARegion( smap ) ) {
+      new = astClone( smap );
+
+/* If the result is a parallel CmpMap, get its two components and check
+   they are Regions. If so, and if they are not the same as the original
+   two component Regions, form a new Prism from them. */
+   } else if( astIsACmpMap( smap ) ) {
+      astDecompose( smap, &map1, &map2, &series, &invert1, &invert2  );
+      if( ! series && astIsARegion( map1 ) && astIsARegion( map2 ) ) {
+         if( (AstRegion *) map1 != reg1 || (AstRegion *) map2 != reg2 ) {
+            new = (AstRegion *) astPrism( (AstRegion *) map1,
+                                          (AstRegion *) map2, "", status );
+         }
+      }
+
+/* Free resources */
+      map1 = astAnnul( map1 );
+      map2 = astAnnul( map2 );
+   }
+
+   smap = astAnnul( smap );
+
+/* If the above produced a simplified Region, map it into the current Frame
+   of "this" and simplify it. */
+   if( new ) {
+      new2 = astMapRegion( new, bcmap, cfrm );
+      (void) astAnnul( new );
+      new = astSimplify( new2 );
+      new2 = astAnnul( new2 );
+
+/* If the above did not produced a result, try a different approach. */
+   } else {
+
+/* Get the number of axes in each component Region. */
+      nax1 = astGetNaxes( reg1 );
+      nax2 = astGetNaxes( reg2 );
+
+/* Use astMapSplit to see if the axes of the first component Region correspond
+   to a distinct set of axes within the current Frame. If this is the case,
+   then a Mapping is returned by astMapSplit which  maps the axes of the first
+   component Region into the corresponding current Frame axes. Also returned
+   is a list of the axes within the current Frame which correspnd to the
+   axes of the first component Region. */
+      nmap1 = NULL;
+      axout1 = NULL;
+      axin = astMalloc( sizeof( int )*(size_t)nax1 );
+      if( astOK ) {
+         for( i = 0; i < nax1; i++ ) axin[ i ] = i;
+         axout1 = astMapSplit( bcmap, nax1, axin, &nmap1 );
+         axin = astFree( axin );
+      }
+
+/* Do the same for the second component. */
+      nmap2 = NULL;
+      axout2 = NULL;
+      axin = astMalloc( sizeof( int )*(size_t)nax2 );
+      if( astOK ) {
+         for( i = 0; i < nax2; i++ ) axin[ i ] = i + nax1;
+         axout2 = astMapSplit( bcmap, nax2, axin, &nmap2 );
+         axin = astFree( axin );
+      }
+
+/* Assume for the moment that the component Regions cannot be simplified.
+   In this case we will use a clone of the supplied Prism. */
+      new = astClone( this_mapping );
+
+/* Determine the number of outputs from these Mappings. */
+      if( nmap1 ){
+         naxout1 = astGetNout( nmap1 );
+      } else {
+         naxout1 = 0;
+      }
+      if( nmap2 ){
+         naxout2 = astGetNout( nmap2 );
+      } else {
+         naxout2 = 0;
+      }
+
+/* Determine the number of axes in the current Frame of the Prism. */
+      naxt = astGetNout( bcmap );
+
+/* If the second component does not contribute any axes to the total
+   Prism, we can ignore it. */
+      if( naxout1 == naxt && naxout2 == 0 ) {
+         newfrm1 = astPickAxes( cfrm, naxout1, axout1, NULL );
+         newreg1 = astMapRegion( reg1, nmap1, newfrm1 );
+         (void) astAnnul( new );
+         new = astSimplify( newreg1 );
+         if( neg ) astNegate( new );
+         perm = astMalloc( sizeof( int )*(size_t) ( naxout1 ) );
+         if( astOK ) {
+            for( i = 0; i < naxout1; i++ ) perm[ i ] = axout1[ i ];
+            astPermAxes( new, perm );
+            perm = astFree( perm );
+         }
+         newfrm1 = astAnnul( newfrm1 );
+         newreg1 = astAnnul( newreg1 );
+
+/* If the first component does not contribute any axes to the total
+   Prism, we can ignore it. */
+      } else if( naxout1 == 0 && naxout2 == naxt ) {
+         newfrm2 = astPickAxes( cfrm, naxout2, axout2, NULL );
+         newreg2 = astMapRegion( reg2, nmap2, newfrm2 );
+         (void) astAnnul( new );
+         new = astSimplify( newreg2 );
+         if( neg ) astNegate( new );
+         perm = astMalloc( sizeof( int )*(size_t) ( naxout2 ) );
+         if( astOK ) {
+            for( i = 0; i < naxout2; i++ ) perm[ i ] = axout2[ i ];
+            astPermAxes( new, perm );
+            perm = astFree( perm );
+         }
+         newfrm2 = astAnnul( newfrm2 );
+         newreg2 = astAnnul( newreg2 );
+
+/* If both component Regions correspond to a distinct subspace within the
+   current Frame, then we can try to express each component Region within
+   the current Frame. */
+      } else if( nmap1 && nmap2 ) {
+
+/* Create a Frame representing the subspace of the current Frame which
+   corresponds to the axes of the first component Region. */
+         newfrm1 = astPickAxes( cfrm, naxout1, axout1, NULL );
+
+/* Remap the first component Region so that it represents an area in this
+   subspace. */
+         newreg1 = astMapRegion( reg1, nmap1, newfrm1 );
+
+/* Attempt to simplify the remapped Region. */
+         snewreg1 = astSimplify( newreg1 );
+
+/* Do the same for the second component Region. */
+         naxout2 = astGetNout( nmap2 );
+         newfrm2 = astPickAxes( cfrm, naxout2, axout2, NULL );
+         newreg2 = astMapRegion( reg2, nmap2, newfrm2 );
+         snewreg2 = astSimplify( newreg2 );
+
+/* If either component Region was simplified, create a new Prism from the
+   simplified Regions. */
+         if( snewreg1 != newreg1 || snewreg2 != newreg2 ) {
+            (void) astAnnul( new );
+            new = (AstRegion *) astPrism( snewreg1, snewreg2, "", status );
+
+/* Ensure the new Prism has the same Negated attribute as the original. */
+            if( neg ) astNegate( new );
+
+/* Ensure that the new Prism has the same axis order as the original
+   current Frame. */
+            perm = astMalloc( sizeof( int )*(size_t) ( naxout1 + naxout2 ) );
+            if( astOK ) {
+               for( i = 0; i < naxout1; i++ ) perm[ i ] = axout1[ i ];
+               for( ; i < naxout1 + naxout2; i++ ) perm[ i ] = axout2[ i - naxout1 ];
+               astPermAxes( new, perm );
+               perm = astFree( perm );
+            }
+         }
+
+/* Free resources. */
+         newfrm1 = astAnnul( newfrm1 );
+         newfrm2 = astAnnul( newfrm2 );
+         newreg1 = astAnnul( newreg1 );
+         newreg2 = astAnnul( newreg2 );
+         snewreg1 = astAnnul( snewreg1 );
+         snewreg2 = astAnnul( snewreg2 );
+      }
+
+/* Free resources. */
+      if( axout1 ) axout1 = astFree( axout1 );
+      if( axout2 ) axout2 = astFree( axout2 );
+      if( nmap1 ) nmap1 = astAnnul( nmap1 );
+      if( nmap2 ) nmap2 = astAnnul( nmap2 );
+   }
+
+/* If we have created a new Region, ensure any user-supplied uncertainty
+   that has been stored explicitly with the supplied Prism is passed on
+   to the new Region. */
+   if( new ) {
+      if( astTestUnc( reg ) ) {
+         unc = astGetUnc( reg, 0 );
+         astSetUnc( new, unc );
+      }
+
+/* Now invoke the parent Simplify method inherited from the Region class.
+   This will simplify the encapsulated FrameSet and uncertainty Region. */
+      result = (*parent_simplify)( (AstMapping *) new, status );
+      new = astAnnul( new );
+   }
+
+/* Free resources. */
+   reg1 = astAnnul( reg1 );
+   reg2 = astAnnul( reg2 );
+   cfrm = astAnnul( cfrm );
+   bcmap = astAnnul( bcmap );
+
+/* If any simplification could be performed, copy Region attributes from
+   the supplied Region to the returned Region, and return a pointer to it. */
+   if( result != this_mapping ) astRegOverlay( result, (AstRegion *) this_mapping, 0 );
+
+/* If an error occurred, annul the returned Mapping. */
+   if ( !astOK ) result = astAnnul( result );
+
+/* Return the result. */
+   return result;
+}
+
+static AstPointSet *Transform( AstMapping *this_mapping, AstPointSet *in,
+                               int forward, AstPointSet *out, int *status ) {
+/*
+*  Name:
+*     Transform
+
+*  Purpose:
+*     Apply a Prism to transform a set of points.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     AstPointSet *Transform( AstMapping *this, AstPointSet *in,
+*                             int forward, AstPointSet *out, int *status )
+
+*  Class Membership:
+*     Prism member function (over-rides the astTransform method inherited
+*     from the Region class).
+
+*  Description:
+*     This function takes a Prism and a set of points encapsulated in a
+*     PointSet and transforms the points so as to apply the required Region.
+*     This implies applying each of the Prism's component Regions in turn,
+*     either in series or in parallel.
+
+*  Parameters:
+*     this
+*        Pointer to the Prism.
+*     in
+*        Pointer to the PointSet associated with the input coordinate values.
+*     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 Prism 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: */
+   AstCmpMap *map;               /* CmpMap containing component Regions */
+   AstPointSet *psb;             /* Pointer to base Frame PointSet */
+   AstPointSet *pset_tmp;        /* Pointer to PointSet holding base Frame positions*/
+   AstPointSet *result;          /* Pointer to output PointSet */
+   AstPrism *this;               /* Pointer to the Prism structure */
+   AstRegion *reg1;              /* Pointer to first component Region */
+   AstRegion *reg2;              /* Pointer to second component Region */
+   double **ptr_out;             /* Pointer to output coordinate data */
+   double **ptrb;                /* Pointer to base Frame axis values */
+   int coord;                    /* Zero-based index for coordinates */
+   int good;                     /* Is the point inside the Prism? */
+   int ncoord_out;               /* No. of coordinates per output point */
+   int ncoord_tmp;               /* No. of coordinates per base Frame point */
+   int neg;                      /* Has Prism been negated? */
+   int npoint;                   /* No. of points */
+   int point;                    /* Loop counter for points */
+
+/* Initialise. */
+   result = NULL;
+
+/* Check the global error status. */
+   if ( !astOK ) return result;
+
+/* Get a Pointer to the Prism structure */
+   this = (AstPrism *) this_mapping;
+
+/* Get the component Regions, and the Negated value for the Prism. */
+   GetRegions( this, &reg1, &reg2, &neg, status );
+
+/* Apply the parent mapping using the stored pointer to the Transform member
+   function inherited from the parent Region class. This function validates
+   all arguments and generates an output PointSet if necessary, containing
+   a copy of the input PointSet. */
+   result = (*parent_transform)( this_mapping, in, forward, out, status );
+
+/* We will now extend the parent astTransform method by performing the
+   calculations needed to generate the output coordinate values. */
+
+/* First use the encapsulated FrameSet in the parent Region structure to
+   transform the supplied positions from the current Frame in the
+   encapsulated FrameSet (the Frame represented by the Prism), to the
+   base Frame (the Frame in which the component Regions are defined). Note,
+   the returned pointer may be a clone of the "in" pointer, and so we
+   must be carefull not to modify the contents of the returned PointSet. */
+   pset_tmp = astRegTransform( this, in, 0, NULL, NULL );
+
+/* Form a parallel CmpMap from the two component Regions. */
+   map = astCmpMap( reg1, reg2, 0, "", status );
+
+/* Apply the Mapping to the PointSet containing positions in the base Frame
+   of the parent Region structure (which is the same as the combination of
+   the current Frames of the component Regions). */
+   psb = astTransform( map, pset_tmp, 1, NULL );
+
+/* Annul the Mapping pointer. */
+   map = astAnnul( map );
+
+/* Determine the numbers of points and coordinates per point for these base
+   Frame PointSets and obtain pointers for accessing the base Frame and output
+   coordinate values. */
+   npoint = astGetNpoint( pset_tmp );
+   ncoord_tmp = astGetNcoord( pset_tmp );
+   ptrb = astGetPoints( psb );
+   ncoord_out = astGetNcoord( result );
+   ptr_out = astGetPoints( result );
+
+/* Perform coordinate arithmetic. */
+/* ------------------------------ */
+   if ( astOK ) {
+      for ( point = 0; point < npoint; point++ ) {
+         good = 1;
+
+         for ( coord = 0; coord < ncoord_tmp; coord++ ) {
+            if( ptrb[ coord ][ point ] == AST__BAD ){
+               good = 0;
+               break;
+            }
+         }
+
+         if( good == neg ) {
+            for ( coord = 0; coord < ncoord_out; coord++ ) {
+               ptr_out[ coord ][ point ] = AST__BAD;
+            }
+         }
+      }
+   }
+
+/* Free resources. */
+   reg1 = astAnnul( reg1 );
+   reg2 = astAnnul( reg2 );
+   psb = astAnnul( psb );
+   pset_tmp = astAnnul( pset_tmp );
+
+/* If an error occurred, clean up by deleting the output PointSet (if
+   allocated by this function) and setting a NULL result pointer. */
+   if ( !astOK ) {
+      if ( !out ) result = astDelete( result );
+      result = NULL;
+   }
+
+/* Return a pointer to the output PointSet. */
+   return result;
+}
+
+/* Copy constructor. */
+/* ----------------- */
+static void Copy( const AstObject *objin, AstObject *objout, int *status ) {
+/*
+*  Name:
+*     Copy
+
+*  Purpose:
+*     Copy constructor for Prism objects.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     void Copy( const AstObject *objin, AstObject *objout, int *status )
+
+*  Description:
+*     This function implements the copy constructor for Prism 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, including a copy of the component
+*     Regions within the Prism.
+*/
+
+/* Local Variables: */
+   AstPrism *in;                /* Pointer to input Prism */
+   AstPrism *out;               /* Pointer to output Prism */
+
+/* Check the global error status. */
+   if ( !astOK ) return;
+
+/* Obtain pointers to the input and output Prisms. */
+   in = (AstPrism *) objin;
+   out = (AstPrism *) objout;
+
+/* For safety, start by clearing any references to the input component
+   Regions from the output Prism. */
+   out->region1 = NULL;
+   out->region2 = NULL;
+
+/* Make copies of these Regions and store pointers to them in the output
+   Prism structure. */
+   out->region1 = astCopy( in->region1 );
+   out->region2 = astCopy( in->region2 );
+}
+
+/* Destructor. */
+/* ----------- */
+static void Delete( AstObject *obj, int *status ) {
+/*
+*  Name:
+*     Delete
+
+*  Purpose:
+*     Destructor for Prism objects.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     void Delete( AstObject *obj, int *status )
+
+*  Description:
+*     This function implements the destructor for Prism 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: */
+   AstPrism *this;              /* Pointer to Prism */
+
+/* Obtain a pointer to the Prism structure. */
+   this = (AstPrism *) obj;
+
+/* Annul the pointers to the component Regions. */
+   this->region1 = astAnnul( this->region1 );
+   this->region2 = astAnnul( this->region2 );
+}
+
+/* Dump function. */
+/* -------------- */
+static void Dump( AstObject *this_object, AstChannel *channel, int *status ) {
+/*
+*  Name:
+*     Dump
+
+*  Purpose:
+*     Dump function for Prism objects.
+
+*  Type:
+*     Private function.
+
+*  Synopsis:
+*     void Dump( AstObject *this, AstChannel *channel, int *status )
+
+*  Description:
+*     This function implements the Dump function which writes out data
+*     for the Prism class to an output Channel.
+
+*  Parameters:
+*     this
+*        Pointer to the Prism 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 Variables: */
+   AstPrism *this;               /* Pointer to the Prism structure */
+
+/* Check the global error status. */
+   if ( !astOK ) return;
+
+/* Obtain a pointer to the Prism structure. */
+   this = (AstPrism *) this_object;
+
+/* Write out values representing the instance variables for the Prism
+   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. */
+
+/* First Region. */
+/* -------------- */
+   astWriteObject( channel, "RegionA", 1, 1, this->region1,
+                   "First component Region" );
+
+/* Second Region. */
+/* --------------- */
+   astWriteObject( channel, "RegionB", 1, 1, this->region2,
+                   "Second component Region" );
+}
+
+/* Standard class functions. */
+/* ========================= */
+/* Implement the astIsAPrism and astCheckPrism functions using the
+   macros defined for this purpose in the "object.h" header file. */
+astMAKE_ISA(Prism,Region)
+astMAKE_CHECK(Prism)
+
+AstPrism *astPrism_( void *region1_void, void *region2_void,
+                     const char *options, int *status, ...) {
+/*
+*+
+*  Name:
+*     astPrism
+
+*  Purpose:
+*     Create a Prism.
+
+*  Type:
+*     Protected function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     AstPrism *astPrism( AstRegion *region1, AstRegion *region2,
+*                         const char *options, ..., int *status )
+
+*  Class Membership:
+*     Prism constructor.
+
+*  Description:
+*     This function creates a new Prism and optionally initialises its
+*     attributes.
+
+*  Parameters:
+*     region1
+*        Pointer to the Region to be extruded.
+*     region2
+*        Pointer to the Region defining the extent of the extrusion.
+*     options
+*        Pointer to a null terminated string containing an optional
+*        comma-separated list of attribute assignments to be used for
+*        initialising the new Prism. The syntax used is the same as for the
+*        astSet method and may include "printf" format specifiers identified
+*        by "%" symbols in the normal way.
+*     status
+*        Pointer to the inherited status variable.
+*     ...
+*        If the "options" string contains "%" format specifiers, then an
+*        optional list of arguments may follow it in order to supply values to
+*        be substituted for these specifiers. The rules for supplying these
+*        are identical to those for the astSet method (and for the C "printf"
+*        function).
+
+*  Returned Value:
+*     A pointer to the new Prism.
+
+*  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.
+*-
+
+*  Implementation Notes:
+*     - This function implements the basic Prism constructor which is
+*     available via the protected interface to the Prism class.  A
+*     public interface is provided by the astPrismId_ function.
+*     - Because this function has a variable argument list, it is
+*     invoked by a macro that evaluates to a function pointer (not a
+*     function invocation) and no checking or casting of arguments is
+*     performed before the function is invoked. Because of this, the
+*     "region1" and "region2" parameters are of type (void *) and are
+*     converted and validated within the function itself.
+*/
+
+/* Local Variables: */
+   astDECLARE_GLOBALS            /* Pointer to thread-specific global data */
+   AstPrism *new;                  /* Pointer to new Prism */
+   AstRegion *region1;             /* Pointer to first Region structure */
+   AstRegion *region2;             /* Pointer to second Region structure */
+   va_list args;                   /* Variable argument list */
+
+/* Initialise. */
+   new = NULL;
+
+/* Get a pointer to the thread specific global data structure. */
+   astGET_GLOBALS(NULL);
+
+/* Check the global status. */
+   if ( !astOK ) return new;
+
+/* Obtain and validate pointers to the Region structures provided. */
+   region1 = astCheckRegion( region1_void );
+   region2 = astCheckRegion( region2_void );
+   if ( astOK ) {
+
+/* Initialise the Prism, allocating memory and initialising the
+   virtual function table as well if necessary. */
+      new = astInitPrism( NULL, sizeof( AstPrism ), !class_init,
+                          &class_vtab, "Prism", region1, region2 );
+
+/* 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 Prism'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 Prism. */
+   return new;
+}
+
+AstPrism *astPrismId_( void *region1_void, void *region2_void,
+                       const char *options, ... ) {
+/*
+*++
+*  Name:
+c     astPrism
+f     AST_PRISM
+
+*  Purpose:
+*     Create a Prism.
+
+*  Type:
+*     Public function.
+
+*  Synopsis:
+c     #include "prism.h"
+c     AstPrism *astPrism( AstRegion *region1, AstRegion *region2,
+c                         const char *options, ... )
+f     RESULT = AST_PRISM( REGION1, REGION2, OPTIONS, STATUS )
+
+*  Class Membership:
+*     Prism constructor.
+
+*  Description:
+*     This function creates a new Prism and optionally initialises
+*     its attributes.
+*
+*     A Prism is a Region which represents an extrusion of an existing Region
+*     into one or more orthogonal dimensions (specified by another Region).
+*     If the Region to be extruded has N axes, and the Region defining the
+*     extrusion has M axes, then the resulting Prism will have (M+N) axes.
+*     A point is inside the Prism if the first N axis values correspond to
+*     a point inside the Region being extruded, and the remaining M axis
+*     values correspond to a point inside the Region defining the extrusion.
+*
+*     As an example, a cylinder can be represented by extruding an existing
+*     Circle, using an Interval to define the extrusion. Ih this case, the
+*     Interval would have a single axis and would specify the upper and
+*     lower limits of the cylinder along its length.
+
+*  Parameters:
+c     region1
+f     REGION1 = INTEGER (Given)
+*        Pointer to the Region to be extruded.
+c     region2
+f     REGION2 = INTEGER (Given)
+*        Pointer to the Region defining the extent of the extrusion.
+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 Prism. 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.
+f        A character string containing an optional comma-separated
+f        list of attribute assignments to be used for initialising the
+f        new Prism. The syntax used is identical to that for the
+f        AST_SET routine.
+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     astPrism()
+f     AST_PRISM = INTEGER
+*        A pointer to the new Prism.
+
+*  Notes:
+*     - Deep copies are taken of the supplied Regions. This means that
+*     any subsequent changes made to the component Regions using the
+*     supplied pointers will have no effect on the Prism.
+*     - 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.
+*--
+
+*  Implementation Notes:
+*     - This function implements the external (public) interface to
+*     the astPrism constructor function. It returns an ID value
+*     (instead of a true C pointer) to external users, and must be
+*     provided because astPrism_ has a variable argument list which
+*     cannot be encapsulated in a macro (where this conversion would
+*     otherwise occur).
+*     - Because no checking or casting of arguments is performed
+*     before the function is invoked, the "region1" and "region2" parameters
+*     are of type (void *) and are converted from an ID value to a
+*     pointer and validated within the function itself.
+*     - The variable argument list also prevents this function from
+*     invoking astPrism_ directly, so it must be a re-implementation
+*     of it in all respects, except for the conversions between IDs
+*     and pointers on input/output of Objects.
+*/
+
+/* Local Variables: */
+   astDECLARE_GLOBALS              /* Pointer to thread-specific global data */
+   AstPrism *new;                  /* Pointer to new Prism */
+   AstRegion *region1;             /* Pointer to first Region structure */
+   AstRegion *region2;             /* Pointer to second Region structure */
+   int *status;                    /* Pointer to inherited status value */
+   va_list args;                   /* Variable argument list */
+
+/* Get a pointer to the thread specific global data structure. */
+   astGET_GLOBALS(NULL);
+
+/* Initialise. */
+   new = NULL;
+
+/* Get a pointer to the inherited status value. */
+   status = astGetStatusPtr;
+
+/* Check the global status. */
+   if ( !astOK ) return new;
+
+/* Obtain the Region pointers from the ID's supplied and validate the
+   pointers to ensure they identify valid Regions. */
+   region1 = astVerifyRegion( astMakePointer( region1_void ) );
+   region2 = astVerifyRegion( astMakePointer( region2_void ) );
+   if ( astOK ) {
+
+/* Initialise the Prism, allocating memory and initialising the
+   virtual function table as well if necessary. */
+      new = astInitPrism( NULL, sizeof( AstPrism ), !class_init,
+                          &class_vtab, "Prism", region1, region2 );
+
+/* 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 Prism'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 Prism. */
+   return astMakeId( new );
+}
+
+AstPrism *astInitPrism_( void *mem, size_t size, int init, AstPrismVtab *vtab,
+                         const char *name, AstRegion *region1,
+                         AstRegion *region2, int *status ) {
+/*
+*+
+*  Name:
+*     astInitPrism
+
+*  Purpose:
+*     Initialise a Prism.
+
+*  Type:
+*     Protected function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     AstPrism *astInitPrism_( void *mem, size_t size, int init,
+*                              AstPrismVtab *vtab, const char *name,
+*                              AstRegion *region1, AstRegion *region2 )
+
+*  Class Membership:
+*     Prism initialiser.
+
+*  Description:
+*     This function is provided for use by class implementations to initialise
+*     a new Prism object. It allocates memory (if necessary) to
+*     accommodate the Prism plus any additional data associated with the
+*     derived class. It then initialises a Prism 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 Prism at the start of
+*     the memory passed via the "vtab" parameter.
+
+*  Parameters:
+*     mem
+*        A pointer to the memory in which the Prism is to be initialised.
+*        This must be of sufficient size to accommodate the Prism data
+*        (sizeof(Prism)) 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 Prism (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
+*        Prism structure, so a valid value must be supplied even if not
+*        required for allocating memory.
+*     init
+*        A logical flag indicating if the Prism'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 Prism.
+*     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 Object
+*        astClass function).
+*     region1
+*        Pointer to the first Region.
+*     region2
+*        Pointer to the second Region.
+
+*  Returned Value:
+*     A pointer to the new Prism.
+
+*  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: */
+   AstPrism *new;                /* Pointer to new Prism */
+   AstFrame *frm1;               /* Frame encapsulated by 1st Region */
+   AstFrame *frm2;               /* Frame encapsulated by 2nd Region */
+   AstFrame *frm;                /* CmpFrame formed from frm1 and frm2 */
+   AstMapping *map;              /* Mapping between two supplied Regions */
+   AstRegion *reg1;              /* Copy of first supplied Region */
+   AstRegion *reg2;              /* Copy of second supplied Region */
+
+/* Check the global status. */
+   if ( !astOK ) return NULL;
+
+/* If necessary, initialise the virtual function table. */
+   if ( init ) astInitPrismVtab( vtab, name );
+
+/* Initialise. */
+   new = NULL;
+   reg2 = NULL;
+
+/* Take a copy of the two supplied Regions. */
+   reg1 = astCopy( region1 );
+   reg2 = astCopy( region2 );
+
+/* Form a CmpFrame representing the combined Frame of these two Regions. */
+   frm1 = astRegFrame( reg1 );
+   frm2 = astRegFrame( reg2 );
+   frm = (AstFrame *) astCmpFrame( frm1, frm2, "", status );
+
+/* Initialise a Region structure (the parent class) as the first component
+   within the Prism structure, allocating memory if necessary. A NULL
+   PointSet is suppled as the two component Regions will perform the function
+   of defining the Region shape. The base Frame of the FrameSet in the
+   parent Region structure will be the CmpFrame formed from the two component
+   Regions. */
+   if ( astOK ) {
+      new = (AstPrism *) astInitRegion( mem, size, 0, (AstRegionVtab *) vtab,
+                                        name, frm, NULL, NULL );
+
+/* Initialise the Prism data. */
+/* --------------------------- */
+/* Store pointers to the component Regions. */
+      new->region1 = reg1;
+      new->region2 = reg2;
+
+/* If the base->current Mapping in the FrameSet within a component Region
+   is a UnitMap, then the FrameSet does not need to be included in the
+   Dump of the new Prism. Set the RegionFS attribute of the component
+   Region to zero to flag this. */
+      map = astGetMapping( reg1->frameset, AST__BASE, AST__CURRENT );
+      if( astIsAUnitMap( map ) ) astSetRegionFS( reg1, 0 );
+      map = astAnnul( map );
+
+      map = astGetMapping( reg2->frameset, AST__BASE, AST__CURRENT );
+      if( astIsAUnitMap( map ) ) astSetRegionFS( reg2, 0 );
+      map = astAnnul( map );
+
+/* If an error occurred, clean up by annulling the Region pointers and
+   deleting the new object. */
+      if ( !astOK ) {
+         new->region1 = astAnnul( new->region1 );
+         new->region2 = astAnnul( new->region2 );
+         new = astDelete( new );
+      }
+   }
+
+/* Free resources */
+   frm = astAnnul( frm );
+   frm1 = astAnnul( frm1 );
+   frm2 = astAnnul( frm2 );
+
+/* Return a pointer to the new object. */
+   return new;
+}
+
+AstPrism *astLoadPrism_( void *mem, size_t size, AstPrismVtab *vtab,
+                         const char *name, AstChannel *channel, int *status ) {
+/*
+*+
+*  Name:
+*     astLoadPrism
+
+*  Purpose:
+*     Load a Prism.
+
+*  Type:
+*     Protected function.
+
+*  Synopsis:
+*     #include "prism.h"
+*     AstPrism *astLoadPrism( void *mem, size_t size, AstPrismVtab *vtab,
+*                             const char *name, AstChannel *channel )
+
+*  Class Membership:
+*     Prism loader.
+
+*  Description:
+*     This function is provided to load a new Prism 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
+*     Prism 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 Prism at the start of the memory
+*     passed via the "vtab" parameter.
+
+
+*  Parameters:
+*     mem
+*        A pointer to the memory into which the Prism is to be
+*        loaded.  This must be of sufficient size to accommodate the
+*        Prism data (sizeof(Prism)) 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 Prism (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 Prism 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(AstPrism) is used instead.
+*     vtab
+*        Pointer to the start of the virtual function table to be
+*        associated with the new Prism. If this is NULL, a pointer to
+*        the (static) virtual function table for the Prism 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 "Prism" is used instead.
+
+*  Returned Value:
+*     A pointer to the new Prism.
+
+*  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: */
+   astDECLARE_GLOBALS      /* Pointer to thread-specific global data */
+   AstFrame *cfrm;         /* Frame containing required axes */
+   AstFrame *f1;           /* Base Frame in parent Region */
+   AstPrism *new;          /* Pointer to the new Prism */
+   AstRegion *creg;        /* Pointer to component Region */
+   int *axes;              /* Pointer to array of axis indices */
+   int i;                  /* Loop count */
+   int nax1;               /* No.of axes in 1st component Frame */
+   int nax2;               /* No.of axes in 2nd component Frame */
+
+/* Initialise. */
+   new = NULL;
+
+/* Check the global error status. */
+   if ( !astOK ) return new;
+
+/* Get a pointer to the thread specific global data structure. */
+   astGET_GLOBALS(channel);
+
+/* If a NULL virtual function table has been supplied, then this is
+   the first loader to be invoked for this Prism. In this case the
+   Prism belongs to this class, so supply appropriate values to be
+   passed to the parent class loader (and its parent, etc.). */
+   if ( !vtab ) {
+      size = sizeof( AstPrism );
+      vtab = &class_vtab;
+      name = "Prism";
+
+/* If required, initialise the virtual function table for this class. */
+      if ( !class_init ) {
+         astInitPrismVtab( 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 Prism. */
+   new = astLoadRegion( mem, size, (AstRegionVtab *) 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, "Prism" );
+
+/* 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. */
+
+/* First Region. */
+/* -------------- */
+      new->region1 = astReadObject( channel, "regiona", NULL );
+
+/* Second Region. */
+/* --------------- */
+      new->region2 = astReadObject( channel, "regionb", NULL );
+
+/* Either component Region may currently contain a dummy FrameSet rather than
+   the correct FrameSet (see the Dump function for this class). In this case,
+   the correct FrameSet will have copies of selected axes from the base Frame
+   of the new Prism as both its current and base Frames, and these are
+   connected by a UnitMap (this is equivalent to a FrameSet containing a
+   single Frame). However if the new Prism being loaded has itself got a dummy
+   FrameSet, then we do not do this since we do not yet know what the correct
+   FrameSet is. In this case we wait until the parent Region invokes the
+   astSetRegFS method on the new Prism. */
+      if( !astRegDummyFS( new ) ) {
+         f1 = astGetFrame( ((AstRegion *) new)->frameset, AST__BASE );
+
+         creg = new->region1;
+         nax1 = astGetNaxes( creg );
+         if( astRegDummyFS( creg ) ) {
+            axes = astMalloc( sizeof( int )*(size_t) nax1 );
+            if( astOK ) for( i = 0; i < nax1; i++ ) axes[ i ] = i;
+            cfrm = astPickAxes( f1, nax1, axes, NULL );
+            astSetRegFS( creg, cfrm );
+            axes = astFree( axes );
+            cfrm = astAnnul( cfrm );
+         }
+
+         creg = new->region2;
+         if( astRegDummyFS( creg ) ) {
+            nax2 = astGetNaxes( creg );
+            axes = astMalloc( sizeof( int )*(size_t) nax2 );
+            if( astOK ) for( i = 0; i < nax2; i++ ) axes[ i ] = nax1 + i;
+            cfrm = astPickAxes( f1, nax2, axes, NULL );
+            astSetRegFS( creg, cfrm );
+            axes = astFree( axes );
+            cfrm = astAnnul( cfrm );
+         }
+
+         f1 = astAnnul( f1 );
+      }
+
+/* If an error occurred, clean up by deleting the new Prism. */
+      if ( !astOK ) new = astDelete( new );
+   }
+
+/* Return the new Prism pointer. */
+   return new;
+}
+
+/* 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. */
+
+/* None. */
+
+
+