rfa 0.5.9

A port ERFA to Rust.
Documentation 
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use crate::vector_matrix::{angle_ops::{anp::*, anpm::*,}, matrix_vec_prod::*, spherical_cartesian::{s2c::s2c, c2s::*} };
///  Transformation from ICRS to Galactic Coordinates.
///
///  Given:
///     dr     double      ICRS right ascension (radians)
///     dd     double      ICRS declination (radians)
///
///  Returned:
///     dl     double      galactic longitude (radians)
///     db     double      galactic latitude (radians)
///
///  Notes:
///
///  1) The IAU 1958 system of Galactic coordinates was defined with
///     respect to the now obsolete reference system FK4 B1950.0.  When
///     interpreting the system in a modern context, several factors have
///     to be taken into account:
///
///     . The inclusion in FK4 positions of the E-terms of aberration.
///
///     . The distortion of the FK4 proper motion system by differential
///       Galactic rotation.
///
///     . The use of the B1950.0 equinox rather than the now-standard
///       J2000.0.
///
///     . The frame bias between ICRS and the J2000.0 mean place system.
///
///     The Hipparcos Catalogue (Perryman & ESA 1997) provides a rotation
///     matrix that transforms directly between ICRS and Galactic
///     coordinates with the above factors taken into account.  The
///     matrix is derived from three angles, namely the ICRS coordinates
///     of the Galactic pole and the longitude of the ascending node of
///     the galactic equator on the ICRS equator.  They are given in
///     degrees to five decimal places and for canonical purposes are
///     regarded as exact.  In the Hipparcos Catalogue the matrix
///     elements are given to 10 decimal places (about 20 microarcsec).
///     In the present ERFA function the matrix elements have been
///     recomputed from the canonical three angles and are given to 30
///     decimal places.
///
///  2) The inverse transformation is performed by the function eraG2icrs.
///
///  Called:
///     eraAnp       normalize angle into range 0 to 2pi
///     eraAnpm      normalize angle into range +/- pi
///     eraS2c       spherical coordinates to unit vector
///     eraRxp       product of r-matrix and p-vector
///     eraC2s       p-vector to spherical
///
///  Reference:
///     Perryman M.A.C. & ESA, 1997, ESA SP-1200, The Hipparcos and Tycho
///     catalogues.  Astrometric and photometric star catalogues
///     derived from the ESA Hipparcos Space Astrometry Mission.  ESA
///     Publications Division, Noordwijk, Netherlands.
///
///  This revision:   2021 January 25
pub fn icrs2g(dr: f64, dd: f64, dl:&mut f64, db:&mut f64)
{
    let mut v1 = [0.0; 3]; let mut v2=[0.0; 3];
 
 /*
 ///  L2,B2 system of galactic coordinates in the form presented in the
 ///  Hipparcos Catalogue.  In degrees:
 ///
 ///  P = 192.85948    right ascension of the Galactic north pole in ICRS
 ///  Q =  27.12825    declination of the Galactic north pole in ICRS
 ///  R =  32.93192    Galactic longitude of the ascending node of
 ///                   the Galactic equator on the ICRS equator
 ///
 ///  ICRS to galactic rotation matrix, obtained by computing
 ///  R_3(-R) R_1(pi/2-Q) R_3(pi/2+P) to the full precision shown:
 */
const R: [[f64;3];3] =[[ -0.054875560416215368492398900454,
                         -0.873437090234885048760383168409,
                         -0.483835015548713226831774175116 ],
                       [ 0.494109427875583673525222371358,
                         -0.444829629960011178146614061616,
                         0.746982244497218890527388004556 ],
                       [ -0.867666149019004701181616534570,
                         -0.198076373431201528180486091412,
                         0.455983776175066922272100478348 ] ];
 
 
 /* Spherical to Cartesian. */
    s2c(dr, dd, &mut v1);
 
 /* ICRS to Galactic. */
    rxp(&R, &v1, &mut v2);
 
 /* Cartesian to spherical. */
    c2s(&v2, dl, db);
 
 /* Express in conventional ranges. */
    *dl = anp(*dl);
    *db = anpm(*db);
 
 /* Finished. */
 
 }