path: root/ast/erfa/apio13.c

#include "erfa.h"

int eraApio13(double utc1, double utc2, double dut1,
              double elong, double phi, double hm, double xp, double yp,
              double phpa, double tc, double rh, double wl,
              eraASTROM *astrom)
/*
**  - - - - - - - - - -
**   e r a A p i o 1 3
**  - - - - - - - - - -
**
**  For a terrestrial observer, prepare star-independent astrometry
**  parameters for transformations between CIRS and observed
**  coordinates.  The caller supplies UTC, site coordinates, ambient air
**  conditions and observing wavelength.
**
**  Given:
**     utc1   double      UTC as a 2-part...
**     utc2   double      ...quasi Julian Date (Notes 1,2)
**     dut1   double      UT1-UTC (seconds)
**     elong  double      longitude (radians, east +ve, Note 3)
**     phi    double      geodetic latitude (radians, Note 3)
**     hm     double      height above ellipsoid (m, geodetic Notes 4,6)
**     xp,yp  double      polar motion coordinates (radians, Note 5)
**     phpa   double      pressure at the observer (hPa = mB, Note 6)
**     tc     double      ambient temperature at the observer (deg C)
**     rh     double      relative humidity at the observer (range 0-1)
**     wl     double      wavelength (micrometers, Note 7)
**
**  Returned:
**     astrom eraASTROM*  star-independent astrometry parameters:
**      pmt    double       unchanged
**      eb     double[3]    unchanged
**      eh     double[3]    unchanged
**      em     double       unchanged
**      v      double[3]    unchanged
**      bm1    double       unchanged
**      bpn    double[3][3] unchanged
**      along  double       longitude + s' (radians)
**      xpl    double       polar motion xp wrt local meridian (radians)
**      ypl    double       polar motion yp wrt local meridian (radians)
**      sphi   double       sine of geodetic latitude
**      cphi   double       cosine of geodetic latitude
**      diurab double       magnitude of diurnal aberration vector
**      eral   double       "local" Earth rotation angle (radians)
**      refa   double       refraction constant A (radians)
**      refb   double       refraction constant B (radians)
**
**  Returned (function value):
**            int         status: +1 = dubious year (Note 2)
**                                 0 = OK
**                                -1 = unacceptable date
**
**  Notes:
**
**  1)  utc1+utc2 is quasi Julian Date (see Note 2), apportioned in any
**      convenient way between the two arguments, for example where utc1
**      is the Julian Day Number and utc2 is the fraction of a day.
**
**      However, JD cannot unambiguously represent UTC during a leap
**      second unless special measures are taken.  The convention in the
**      present function is that the JD day represents UTC days whether
**      the length is 86399, 86400 or 86401 SI seconds.
**
**      Applications should use the function eraDtf2d to convert from
**      calendar date and time of day into 2-part quasi Julian Date, as
**      it implements the leap-second-ambiguity convention just
**      described.
**
**  2)  The warning status "dubious year" flags UTCs that predate the
**      introduction of the time scale or that are too far in the future
**      to be trusted.  See eraDat for further details.
**
**  3)  UT1-UTC is tabulated in IERS bulletins.  It increases by exactly
**      one second at the end of each positive UTC leap second,
**      introduced in order to keep UT1-UTC within +/- 0.9s.  n.b. This
**      practice is under review, and in the future UT1-UTC may grow
**      essentially without limit.
**
**  4)  The geographical coordinates are with respect to the ERFA_WGS84
**      reference ellipsoid.  TAKE CARE WITH THE LONGITUDE SIGN:  the
**      longitude required by the present function is east-positive
**      (i.e. right-handed), in accordance with geographical convention.
**
**  5)  The polar motion xp,yp can be obtained from IERS bulletins.  The
**      values are the coordinates (in radians) of the Celestial
**      Intermediate Pole with respect to the International Terrestrial
**      Reference System (see IERS Conventions 2003), measured along the
**      meridians 0 and 90 deg west respectively.  For many applications,
**      xp and yp can be set to zero.
**
**      Internally, the polar motion is stored in a form rotated onto
**      the local meridian.
**
**  6)  If hm, the height above the ellipsoid of the observing station
**      in meters, is not known but phpa, the pressure in hPa (=mB), is
**      available, an adequate estimate of hm can be obtained from the
**      expression
**
**            hm = -29.3 * tsl * log ( phpa / 1013.25 );
**
**      where tsl is the approximate sea-level air temperature in K
**      (See Astrophysical Quantities, C.W.Allen, 3rd edition, section
**      52).  Similarly, if the pressure phpa is not known, it can be
**      estimated from the height of the observing station, hm, as
**      follows:
**
**            phpa = 1013.25 * exp ( -hm / ( 29.3 * tsl ) );
**
**      Note, however, that the refraction is nearly proportional to the
**      pressure and that an accurate phpa value is important for
**      precise work.
**
**  7)  The argument wl specifies the observing wavelength in
**      micrometers.  The transition from optical to radio is assumed to
**      occur at 100 micrometers (about 3000 GHz).
**
**  8)  It is advisable to take great care with units, as even unlikely
**      values of the input parameters are accepted and processed in
**      accordance with the models used.
**
**  9)  In cases where the caller wishes to supply his own Earth
**      rotation information and refraction constants, the function
**      eraApc can be used instead of the present function.
**
**  10) This is one of several functions that inserts into the astrom
**      structure star-independent parameters needed for the chain of
**      astrometric transformations ICRS <-> GCRS <-> CIRS <-> observed.
**
**      The various functions support different classes of observer and
**      portions of the transformation chain:
**
**          functions         observer        transformation
**
**       eraApcg eraApcg13    geocentric      ICRS <-> GCRS
**       eraApci eraApci13    terrestrial     ICRS <-> CIRS
**       eraApco eraApco13    terrestrial     ICRS <-> observed
**       eraApcs eraApcs13    space           ICRS <-> GCRS
**       eraAper eraAper13    terrestrial     update Earth rotation
**       eraApio eraApio13    terrestrial     CIRS <-> observed
**
**      Those with names ending in "13" use contemporary ERFA models to
**      compute the various ephemerides.  The others accept ephemerides
**      supplied by the caller.
**
**      The transformation from ICRS to GCRS covers space motion,
**      parallax, light deflection, and aberration.  From GCRS to CIRS
**      comprises frame bias and precession-nutation.  From CIRS to
**      observed takes account of Earth rotation, polar motion, diurnal
**      aberration and parallax (unless subsumed into the ICRS <-> GCRS
**      transformation), and atmospheric refraction.
**
**  11) The context structure astrom produced by this function is used
**      by eraAtioq and eraAtoiq.
**
**  Called:
**     eraUtctai    UTC to TAI
**     eraTaitt     TAI to TT
**     eraUtcut1    UTC to UT1
**     eraSp00      the TIO locator s', IERS 2000
**     eraEra00     Earth rotation angle, IAU 2000
**     eraRefco     refraction constants for given ambient conditions
**     eraApio      astrometry parameters, CIRS-observed
**
**  Copyright (C) 2013-2014, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
   int j;
   double tai1, tai2, tt1, tt2, ut11, ut12, sp, theta, refa, refb;


/* UTC to other time scales. */
   j = eraUtctai(utc1, utc2, &tai1, &tai2);
   if ( j < 0 ) return -1;
   j = eraTaitt(tai1, tai2, &tt1, &tt2);
   j = eraUtcut1(utc1, utc2, dut1, &ut11, &ut12);
   if ( j < 0 ) return -1;

/* TIO locator s'. */
   sp = eraSp00(tt1, tt2);

/* Earth rotation angle. */
   theta = eraEra00(ut11, ut12);

/* Refraction constants A and B. */
   eraRefco(phpa, tc, rh, wl, &refa, &refb);

/* CIRS <-> observed astrometry parameters. */
   eraApio(sp, theta, elong, phi, hm, xp, yp, refa, refb, astrom);

/* Return any warning status. */
   return j;

/* Finished. */

}
/*----------------------------------------------------------------------
**  
**  
**  Copyright (C) 2013-2014, NumFOCUS Foundation.
**  All rights reserved.
**  
**  This library is derived, with permission, from the International
**  Astronomical Union's "Standards of Fundamental Astronomy" library,
**  available from http://www.iausofa.org.
**  
**  The ERFA version is intended to retain identical functionality to
**  the SOFA library, but made distinct through different function and
**  file names, as set out in the SOFA license conditions.  The SOFA
**  original has a role as a reference standard for the IAU and IERS,
**  and consequently redistribution is permitted only in its unaltered
**  state.  The ERFA version is not subject to this restriction and
**  therefore can be included in distributions which do not support the
**  concept of "read only" software.
**  
**  Although the intent is to replicate the SOFA API (other than
**  replacement of prefix names) and results (with the exception of
**  bugs;  any that are discovered will be fixed), SOFA is not
**  responsible for any errors found in this version of the library.
**  
**  If you wish to acknowledge the SOFA heritage, please acknowledge
**  that you are using a library derived from SOFA, rather than SOFA
**  itself.
**  
**  
**  TERMS AND CONDITIONS
**  
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**  modification, are permitted provided that the following conditions
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**  
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