testbed/astropy__astropy/cextern/erfa/bpn2xy.c

#include "erfa.h"

void eraBpn2xy(double rbpn[3][3], double *x, double *y)
/*
**  - - - - - - - - - -
**   e r a B p n 2 x y
**  - - - - - - - - - -
**
**  Extract from the bias-precession-nutation matrix the X,Y coordinates
**  of the Celestial Intermediate Pole.
**
**  Given:
**     rbpn      double[3][3]  celestial-to-true matrix (Note 1)
**
**  Returned:
**     x,y       double        Celestial Intermediate Pole (Note 2)
**
**  Notes:
**
**  1) The matrix rbpn transforms vectors from GCRS to true equator (and
**     CIO or equinox) of date, and therefore the Celestial Intermediate
**     Pole unit vector is the bottom row of the matrix.
**
**  2) The arguments x,y are components of the Celestial Intermediate
**     Pole unit vector in the Geocentric Celestial Reference System.
**
**  Reference:
**
**     "Expressions for the Celestial Intermediate Pole and Celestial
**     Ephemeris Origin consistent with the IAU 2000A precession-
**     nutation model", Astron.Astrophys. 400, 1145-1154
**     (2003)
**
**     n.b. The celestial ephemeris origin (CEO) was renamed "celestial
**          intermediate origin" (CIO) by IAU 2006 Resolution 2.
**
**  Copyright (C) 2013-2017, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
/* Extract the X,Y coordinates. */
   *x = rbpn[2][0];
   *y = rbpn[2][1];

   return;

}
/*----------------------------------------------------------------------
**  
**  
**  Copyright (C) 2013-2017, NumFOCUS Foundation.
**  All rights reserved.
**  
**  This library is derived, with permission, from the International
**  Astronomical Union's "Standards of Fundamental Astronomy" library,
**  available from http://www.iausofa.org.
**  
**  The ERFA version is intended to retain identical functionality to
**  the SOFA library, but made distinct through different function and
**  file names, as set out in the SOFA license conditions.  The SOFA
**  original has a role as a reference standard for the IAU and IERS,
**  and consequently redistribution is permitted only in its unaltered
**  state.  The ERFA version is not subject to this restriction and
**  therefore can be included in distributions which do not support the
**  concept of "read only" software.
**  
**  Although the intent is to replicate the SOFA API (other than
**  replacement of prefix names) and results (with the exception of
**  bugs;  any that are discovered will be fixed), SOFA is not
**  responsible for any errors found in this version of the library.
**  
**  If you wish to acknowledge the SOFA heritage, please acknowledge
**  that you are using a library derived from SOFA, rather than SOFA
**  itself.
**  
**  
**  TERMS AND CONDITIONS
**  
**  Redistribution and use in source and binary forms, with or without
**  modification, are permitted provided that the following conditions
**  are met:
**  
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**    notice, this list of conditions and the following disclaimer.
**  
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*/