sofars 0.6.0

Pure Rust implementation of the IAU SOFA library
Documentation 
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use crate::vm::{anp, c2s, rxp, s2c};

use super::{IauAstrom, ab, ldsun};

///  Quick astrometric ICRS −> CIRS
///
///  Quick ICRS to CIRS transformation, given precomputed star-
///  independent astrometry parameters, and assuming zero parallax and
///  proper motion.
///
///  Use of this function is appropriate when efficiency is important and
///  where many star positions are to be transformed for one date.  The
///  star-independent parameters can be obtained by calling one of the
///  functions iauApci[13], iauApcg[13], iauApco[13] or iauApcs[13].
///
///  The corresponding function for the case of non-zero parallax and
///  proper motion is iauAtciq.
///
///  This function is part of the International Astronomical Union's
///  SOFA (Standards of Fundamental Astronomy) software collection.
///
///  Status:  support function.
///
///  Given:
///  ```
///     rc,dc  double     ICRS astrometric RA,Dec (radians)
///     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       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:
///  ```
///     ri,di  double     CIRS RA,Dec (radians)
///  ```
///  Note:
///
///     All the vectors are with respect to BCRS axes.
///
///  References:
///
///     Urban, S. & Seidelmann, P. K. (eds), Explanatory Supplement to
///     the Astronomical Almanac, 3rd ed., University Science Books
///     (2013).
///
///     Klioner, Sergei A., "A practical relativistic model for micro-
///     arcsecond astrometry in space", Astr. J. 125, 1580-1597 (2003).
///
///  Called:
///  ```
///     iauS2c       spherical coordinates to unit vector
///     iauLdsun     light deflection due to Sun
///     iauAb        stellar aberration
///     iauRxp       product of r-matrix and p-vector
///     iauC2s       p-vector to spherical
///     iauAnp       normalize angle into range +/- pi
///  ```
pub fn atciqz(rc: f64, dc: f64, astrom: &mut IauAstrom) -> (f64, f64) {
    /* BCRS coordinate direction (unit vector). */
    let pco = s2c(rc, dc);

    /* Light deflection by the Sun, giving BCRS natural direction. */
    let pnat = ldsun(pco, astrom.eh, astrom.em);

    /* Aberration, giving GCRS proper direction. */
    let ppr = ab(&pnat, &astrom.v, astrom.em, astrom.bm1);

    /* Bias-precession-nutation, giving CIRS proper direction. */
    let mut pi = [0.0; 3];
    rxp(&astrom.bpn, &ppr, &mut pi);

    /* CIRS RA,Dec. */
    let (w, di) = c2s(&pi);
    let ri = anp(w);

    (ri, di)
}