public static function Apcg($date1, $date2, array $ebpv, array $ehp,
          iauASTROM &$astrom) {

    /* Geocentric observer */
    $pv = [ [ 0.0, 0.0, 0.0],
        [ 0.0, 0.0, 0.0]];

    /* Compute the star-independent astrometry parameters. */
    IAU::Apcs($date1, $date2, $pv, $ebpv, $ehp, $astrom);

    /* Finished. */
  }
public static function Apcg($date1, $date2, array $ebpv, array $ehp,
          iauASTROM &$astrom) {

    /* Geocentric observer */
    $pv = [ [ 0.0, 0.0, 0.0],
        [ 0.0, 0.0, 0.0]];

    /* Compute the star-independent astrometry parameters. */
    IAU::Apcs($date1, $date2, $pv, $ebpv, $ehp, $astrom);

    /* Finished. */
  }
public static function Apcg ( $ date1 , $ date2 , array $ ebpv , array $ ehp , iauASTROM & $ astrom ) { /* Geocentric observer */ $ pv = [ [ 0.0 , 0.0 , 0.0 ] , [ 0.0 , 0.0 , 0.0 ] ] ; /* Compute the star-independent astrometry parameters. */ IAU :: Apcs ( $ date1 , $ date2 , $ pv , $ ebpv , $ ehp , $ astrom ) ; /* Finished. */ }
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For a geocentric observer, prepare star-independent astrometry
parameters for transformations between ICRS and GCRS coordinates.
The Earth ephemeris is supplied by the caller.

The parameters produced by this function are required in the
parallax, light deflection and aberration parts of the astrometric
transformation chain.

This function is part of the International Astronomical Union's
SOFA (Standards of Fundamental Astronomy) software collection.

Status:  support function.

Given:
date1  double       TDB as a 2-part...
date2  double       ...Julian Date (Note 1)
ebpv   double[2][3] Earth barycentric pos/vel (au, au/day)
ehp    double[3]    Earth heliocentric position (au)

Returned:
astrom iauASTROM*   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) 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

iauApcg iauApcg13    geocentric      ICRS <-> GCRS
iauApci iauApci13    terrestrial     ICRS <-> CIRS
iauApco iauApco13    terrestrial     ICRS <-> observed
iauApcs iauApcs13    space           ICRS <-> GCRS
iauAper iauAper13    terrestrial     update Earth rotation
iauApio iauApio13    terrestrial     CIRS <-> observed

Those with names ending in "13" use contemporary SOFA 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.

4) The context structure astrom produced by this function is used by
iauAtciq* and iauAticq*.

Called:
iauApcs      astrometry parameters, ICRS-GCRS, space observer

This revision:   2013 October 9

SOFA release 2015-02-09

Copyright (C) 2015 IAU SOFA Board.  See notes at end.
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