apcg13.c

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#include "erfa.h"

void eraApcg13(double date1, double date2, eraASTROM *astrom)
/*
**  - - - - - - - - - -
**   e r a A p c g 1 3
**  - - - - - - - - - -
**
**  For a geocentric observer, prepare star-independent astrometry
**  parameters for transformations between ICRS and GCRS coordinates.
**  The caller supplies the date, and ERFA models are used to predict
**  the Earth ephemeris.
**
**  The parameters produced by this function are required in the
**  parallax, light deflection and aberration parts of the astrometric
**  transformation chain.
**
**  Given:
**     date1  double     TDB as a 2-part...
**     date2  double     ...Julian Date (Note 1)
**
**  Returned:
**     astrom eraASTROM* star-independent astrometry parameters:
**      pmt    double       PM time interval (SSB, Julian years)
**      eb     double[3]    SSB to observer (vector, au)
**      eh     double[3]    Sun to observer (unit vector)
**      em     double       distance from Sun to observer (au)
**      v      double[3]    barycentric observer velocity (vector, c)
**      bm1    double       sqrt(1-|v|^2): reciprocal of Lorenz factor
**      bpn    double[3][3] bias-precession-nutation matrix
**      along  double       unchanged
**      xpl    double       unchanged
**      ypl    double       unchanged
**      sphi   double       unchanged
**      cphi   double       unchanged
**      diurab double       unchanged
**      eral   double       unchanged
**      refa   double       unchanged
**      refb   double       unchanged
**
**  Notes:
**
**  1) The TDB date date1+date2 is a Julian Date, apportioned in any
**     convenient way between the two arguments.  For example,
**     JD(TDB)=2450123.7 could be expressed in any of these ways, among
**     others:
**
**            date1          date2
**
**         2450123.7           0.0       (JD method)
**         2451545.0       -1421.3       (J2000 method)
**         2400000.5       50123.2       (MJD method)
**         2450123.5           0.2       (date & time method)
**
**     The JD method is the most natural and convenient to use in cases
**     where the loss of several decimal digits of resolution is
**     acceptable.  The J2000 method is best matched to the way the
**     argument is handled internally and will deliver the optimum
**     resolution.  The MJD method and the date & time methods are both
**     good compromises between resolution and convenience.  For most
**     applications of this function the choice will not be at all
**     critical.
**
**     TT can be used instead of TDB without any significant impact on
**     accuracy.
**
**  2) All the vectors are with respect to BCRS axes.
**
**  3) In cases where the caller wishes to supply his own Earth
**     ephemeris, the function eraApcg can be used instead of the present
**     function.
**
**  4) 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.
**
**  5) The context structure astrom produced by this function is used by
**     eraAtciq* and eraAticq*.
**
**  Called:
**     eraEpv00     Earth position and velocity
**     eraApcg      astrometry parameters, ICRS-GCRS, geocenter
**
**  Copyright (C) 2013-2015, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
   double ehpv[2][3], ebpv[2][3];

/* Earth barycentric & heliocentric position/velocity (au, au/d). */
   (void) eraEpv00(date1, date2, ehpv, ebpv);

/* Compute the star-independent astrometry parameters. */
   eraApcg(date1, date2, ebpv, ehpv[0], astrom);

/* Finished. */

}
/*----------------------------------------------------------------------
**  
**  
**  Copyright (C) 2013-2015, 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
**  
**  Redistribution and use in source and binary forms, with or without
**  modification, are permitted provided that the following conditions
**  are met:
**  
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**    notice, this list of conditions and the following disclaimer.
**  
**  2 Redistributions in binary form must reproduce the above copyright
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**  
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