sofars 0.6.0

Pure Rust implementation of the IAU SOFA library
Documentation 
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use crate::consts::DAS2R;

///  Frame bias components, IAU 2000
///
///  Frame bias components of IAU 2000 precession-nutation models;  part
///  of the Mathews-Herring-Buffett (MHB2000) nutation series, with
///  additions.
///
///  This function is part of the International Astronomical Union's
///  SOFA (Standards of Fundamental Astronomy) software collection.
///
///  Status:  canonical model.
///
///  Returned:
///     dpsibi,depsbi  double  longitude and obliquity corrections
///     dra            double  the ICRS RA of the J2000.0 mean equinox
///
///  Notes:
///
///  1) The frame bias corrections in longitude and obliquity (radians)
///     are required in order to correct for the offset between the GCRS
///     pole and the mean J2000.0 pole.  They define, with respect to the
///     GCRS frame, a J2000.0 mean pole that is consistent with the rest
///     of the IAU 2000A precession-nutation model.
///
///  2) In addition to the displacement of the pole, the complete
///     description of the frame bias requires also an offset in right
///     ascension.  This is not part of the IAU 2000A model, and is from
///     Chapront et al. (2002).  It is returned in radians.
///
///  3) This is a supplemented implementation of one aspect of the IAU
///     2000A nutation model, formally adopted by the IAU General
///     Assembly in 2000, namely MHB2000 (Mathews et al. 2002).
///
///  References:
///
///     Chapront, J., Chapront-Touze, M. & Francou, G., Astron.
///     Astrophys., 387, 700, 2002.
///
///     Mathews, P.M., Herring, T.A., Buffet, B.A., "Modeling of nutation
///     and precession:  New nutation series for nonrigid Earth and
///     insights into the Earth's interior", J.Geophys.Res., 107, B4,
///     2002.  The MHB2000 code itself was obtained on 2002 September 9
///     from ftp://maia.usno.navy.mil/conv2000/chapter5/IAU2000A.
///
///  This revision:  2021 May 11
///
///  SOFA release 2023-10-11
///
///  Copyright (C) 2023 IAU SOFA Board.  See notes at end.
///
pub fn bi00() -> (f64, f64, f64) {
    /* The frame bias corrections in longitude and obliquity */
    const DPBIAS: f64 = -0.041775 * DAS2R;
    const DEBIAS: f64 = -0.0068192 * DAS2R;

    /* The ICRS RA of the J2000.0 equinox (Chapront et al., 2002) */
    const DRA0: f64 = -0.0146 * DAS2R;

    /* Return the results (which are fixed). */
    let dpsibi = DPBIAS;
    let depsbi = DEBIAS;
    let dra = DRA0;

    (dpsibi, depsbi, dra)
}