#include "sofa.h"

void iauC2ixys(double x, double y, double s, double rc2i[3][3])
/*
**  - - - - - - - - - -
**   i a u C 2 i x y s
**  - - - - - - - - - -
**
**  Form the celestial to intermediate-frame-of-date matrix given the CIP
**  X,Y and the CIO locator s.
**
**  This function is part of the International Astronomical Union's
**  SOFA (Standards Of Fundamental Astronomy) software collection.
**
**  Status:  support function.
**
**  Given:
**     x,y      double         Celestial Intermediate Pole (Note 1)
**     s        double         the CIO locator s (Note 2)
**
**  Returned:
**     rc2i     double[3][3]   celestial-to-intermediate matrix (Note 3)
**
**  Notes:
**
**  1) The Celestial Intermediate Pole coordinates are the x,y
**     components of the unit vector in the Geocentric Celestial
**     Reference System.
**
**  2) The CIO locator s (in radians) positions the Celestial
**     Intermediate Origin on the equator of the CIP.
**
**  3) The matrix rc2i is the first stage in the transformation from
**     celestial to terrestrial coordinates:
**
**        [TRS] = RPOM * R_3(ERA) * rc2i * [CRS]
**
**              = RC2T * [CRS]
**
**     where [CRS] is a vector in the Geocentric Celestial Reference
**     System and [TRS] is a vector in the International Terrestrial
**     Reference System (see IERS Conventions 2003), ERA is the Earth
**     Rotation Angle and RPOM is the polar motion matrix.
**
**  Called:
**     iauIr        initialize r-matrix to identity
**     iauRz        rotate around Z-axis
**     iauRy        rotate around Y-axis
**
**  Reference:
**
**     McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
**     IERS Technical Note No. 32, BKG (2004)
**
**  This revision:  2014 November 7
**
**  SOFA release 2015-02-09
**
**  Copyright (C) 2015 IAU SOFA Board.  See notes at end.
*/
{
   double r2, e, d;


/* Obtain the spherical angles E and d. */
   r2 = x*x + y*y;
   e = (r2 > 0.0) ? atan2(y, x) : 0.0;
   d = atan(sqrt(r2 / (1.0 - r2)));

/* Form the matrix. */
   iauIr(rc2i);
   iauRz(e, rc2i);
   iauRy(d, rc2i);
   iauRz(-(e+s), rc2i);

   return;

/*----------------------------------------------------------------------
**
**  Copyright (C) 2015
**  Standards Of Fundamental Astronomy Board
**  of the International Astronomical Union.
**
**  =====================
**  SOFA Software License
**  =====================
**
**  NOTICE TO USER:
**
**  BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
**  CONDITIONS WHICH APPLY TO ITS USE.
**
**  1. The Software is owned by the IAU SOFA Board ("SOFA").
**
**  2. Permission is granted to anyone to use the SOFA software for any
**     purpose, including commercial applications, free of charge and
**     without payment of royalties, subject to the conditions and
**     restrictions listed below.
**
**  3. You (the user) may copy and distribute SOFA source code to others,
**     and use and adapt its code and algorithms in your own software,
**     on a world-wide, royalty-free basis.  That portion of your
**     distribution that does not consist of intact and unchanged copies
**     of SOFA source code files is a "derived work" that must comply
**     with the following requirements:
**
**     a) Your work shall be marked or carry a statement that it
**        (i) uses routines and computations derived by you from
**        software provided by SOFA under license to you; and
**        (ii) does not itself constitute software provided by and/or
**        endorsed by SOFA.
**
**     b) The source code of your derived work must contain descriptions
**        of how the derived work is based upon, contains and/or differs
**        from the original SOFA software.
**
**     c) The names of all routines in your derived work shall not
**        include the prefix "iau" or "sofa" or trivial modifications
**        thereof such as changes of case.
**
**     d) The origin of the SOFA components of your derived work must
**        not be misrepresented;  you must not claim that you wrote the
**        original software, nor file a patent application for SOFA
**        software or algorithms embedded in the SOFA software.
**
**     e) These requirements must be reproduced intact in any source
**        distribution and shall apply to anyone to whom you have
**        granted a further right to modify the source code of your
**        derived work.
**
**     Note that, as originally distributed, the SOFA software is
**     intended to be a definitive implementation of the IAU standards,
**     and consequently third-party modifications are discouraged.  All
**     variations, no matter how minor, must be explicitly marked as
**     such, as explained above.
**
**  4. You shall not cause the SOFA software to be brought into
**     disrepute, either by misuse, or use for inappropriate tasks, or
**     by inappropriate modification.
**
**  5. The SOFA software is provided "as is" and SOFA makes no warranty
**     as to its use or performance.   SOFA does not and cannot warrant
**     the performance or results which the user may obtain by using the
**     SOFA software.  SOFA makes no warranties, express or implied, as
**     to non-infringement of third party rights, merchantability, or
**     fitness for any particular purpose.  In no event will SOFA be
**     liable to the user for any consequential, incidental, or special
**     damages, including any lost profits or lost savings, even if a
**     SOFA representative has been advised of such damages, or for any
**     claim by any third party.
**
**  6. The provision of any version of the SOFA software under the terms
**     and conditions specified herein does not imply that future
**     versions will also be made available under the same terms and
**     conditions.
*
**  In any published work or commercial product which uses the SOFA
**  software directly, acknowledgement (see www.iausofa.org) is
**  appreciated.
**
**  Correspondence concerning SOFA software should be addressed as
**  follows:
**
**      By email:  sofa@ukho.gov.uk
**      By post:   IAU SOFA Center
**                 HM Nautical Almanac Office
**                 UK Hydrographic Office
**                 Admiralty Way, Taunton
**                 Somerset, TA1 2DN
**                 United Kingdom
**
**--------------------------------------------------------------------*/
}
