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use ;
/// Prepare for ICRS <−> GCRS, geocentric, special
///
/// 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
/// ```