rfa 0.5.9

A port ERFA to Rust.
Documentation 
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use super::apcg::apcg;
use crate::ephemerides::epv00::epv00;
use crate::UrsaASTROM;
/*
**  - - - - - - - - - -
**   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
*/
pub fn apcg13(date1:f64, date2: f64, astrom: &mut UrsaASTROM)
{
   let mut ehpv = [[0.0;3] ;2];
   let mut ebpv = [[0.0;3] ;2];
/* Earth barycentric & heliocentric position/velocity (au, au/d). */
   epv00(date1, date2, &mut ehpv, &mut ebpv);

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

/* Finished. */
}