#include "erfa.h"

void eraFk5hz(double r5, double d5, double date1, double date2,
              double *rh, double *dh)
/*
**  - - - - - - - - -
**   e r a F k 5 h z
**  - - - - - - - - -
**
**  Transform an FK5 (J2000.0) star position into the system of the
**  Hipparcos catalogue, assuming zero Hipparcos proper motion.
**
**  Given:
**     r5           double   FK5 RA (radians), equinox J2000.0, at date
**     d5           double   FK5 Dec (radians), equinox J2000.0, at date
**     date1,date2  double   TDB date (Notes 1,2)
**
**  Returned:
**     rh           double   Hipparcos RA (radians)
**     dh           double   Hipparcos Dec (radians)
**
**  Notes:
**
**  1) This function converts a star position from the FK5 system to
**     the Hipparcos system, in such a way that the Hipparcos proper
**     motion is zero.  Because such a star has, in general, a non-zero
**     proper motion in the FK5 system, the function requires the date
**     at which the position in the FK5 system was determined.
**
**  2) The TT date date1+date2 is a Julian Date, apportioned in any
**     convenient way between the two arguments.  For example,
**     JD(TT)=2450123.7 could be expressed in any of these ways,
**     among others:
**
**            date1          date2
**
**         2450123.7           0.0       (JD method)
**         2451545.0       -1421.3       (J2000 method)
**         2400000.5       50123.2       (MJD method)
**         2450123.5           0.2       (date & time method)
**
**     The JD method is the most natural and convenient to use in
**     cases where the loss of several decimal digits of resolution
**     is acceptable.  The J2000 method is best matched to the way
**     the argument is handled internally and will deliver the
**     optimum resolution.  The MJD method and the date & time methods
**     are both good compromises between resolution and convenience.
**
**  3) The FK5 to Hipparcos transformation is modeled as a pure
**     rotation and spin;  zonal errors in the FK5 catalogue are not
**     taken into account.
**
**  4) The position returned by this function is in the Hipparcos
**     reference system but at date date1+date2.
**
**  5) See also eraFk52h, eraH2fk5, eraHfk5z.
**
**  Called:
**     eraS2c       spherical coordinates to unit vector
**     eraFk5hip    FK5 to Hipparcos rotation and spin
**     eraSxp       multiply p-vector by scalar
**     eraRv2m      r-vector to r-matrix
**     eraTrxp      product of transpose of r-matrix and p-vector
**     eraPxp       vector product of two p-vectors
**     eraC2s       p-vector to spherical
**     eraAnp       normalize angle into range 0 to 2pi
**
**  Reference:
**
**     F.Mignard & M.Froeschle, 2000, Astron.Astrophys. 354, 732-739.
**
**  Copyright (C) 2013-2020, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
   double t, p5e[3], r5h[3][3], s5h[3], vst[3], rst[3][3], p5[3],
          ph[3], w;


/* Interval from given date to fundamental epoch J2000.0 (JY). */
   t = - ((date1 - ERFA_DJ00) + date2) / ERFA_DJY;

/* FK5 barycentric position vector. */
   eraS2c(r5, d5, p5e);

/* FK5 to Hipparcos orientation matrix and spin vector. */
   eraFk5hip(r5h, s5h);

/* Accumulated Hipparcos wrt FK5 spin over that interval. */
   eraSxp(t, s5h, vst);

/* Express the accumulated spin as a rotation matrix. */
   eraRv2m(vst, rst);

/* Derotate the vector's FK5 axes back to date. */
   eraTrxp(rst, p5e, p5);

/* Rotate the vector into the Hipparcos system. */
   eraRxp(r5h, p5, ph);

/* Hipparcos vector to spherical. */
   eraC2s(ph, &w, dh);
   *rh = eraAnp(w);

   return;

}
/*----------------------------------------------------------------------
**  
**  
**  Copyright (C) 2013-2020, 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:
**  
**  1 Redistributions of source code must retain the above copyright
**    notice, this list of conditions and the following disclaimer.
**  
**  2 Redistributions in binary form must reproduce the above copyright
**    notice, this list of conditions and the following disclaimer in
**    the documentation and/or other materials provided with the
**    distribution.
**  
**  3 Neither the name of the Standards Of Fundamental Astronomy Board,
**    the International Astronomical Union nor the names of its
**    contributors may be used to endorse or promote products derived
**    from this software without specific prior written permission.
**  
**  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
**  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
**  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
**  FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
**  COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
**  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
**  BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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**  LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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**  
*/
