File: palEvp.c

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starlink-pal 0.9.8-1
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/*
*+
*  Name:
*     palEvp

*  Purpose:
*     Returns the barycentric and heliocentric velocity and position of the
*     Earth.

*  Language:
*     Starlink ANSI C

*  Type of Module:
*     Library routine

*  Invocation:
*     void palEvp( double date, double deqx, double dvb[3], double dpb[3],
*                  double dvh[3], double dph[3] )

*  Arguments:
*     date = double (Given)
*        TDB (loosely ET) as a Modified Julian Date (JD-2400000.5)
*     deqx = double (Given)
*        Julian epoch (e.g. 2000.0) of mean equator and equinox of the
*        vectors returned.  If deqx <= 0.0, all vectors are referred to the
*        mean equator and equinox (FK5) of epoch date.
*     dvb = double[3] (Returned)
*        Barycentric velocity (AU/s, AU)
*     dpb = double[3] (Returned)
*        Barycentric position (AU/s, AU)
*     dvh = double[3] (Returned)
*        heliocentric velocity (AU/s, AU)
*     dph = double[3] (Returned)
*        Heliocentric position (AU/s, AU)

*  Description:
*     Returns the barycentric and heliocentric velocity and position of the
*     Earth at a given epoch, given with respect to a specified equinox.
*     For information about accuracy, see the function eraEpv00.

*  Authors:
*     PTW: Pat Wallace (STFC)
*     {enter_new_authors_here}

*  History:
*     2012-02-13 (PTW):
*        Initial version.
*        Adapted with permission from the Fortran SLALIB library.
*     {enter_further_changes_here}

*  Copyright:
*     Copyright (C) 2005 Patrick T. Wallace
*     Copyright (C) 2012 Science and Technology Facilities Council.
*     All Rights Reserved.

*  Licence:
*     This program is free software: you can redistribute it and/or
*     modify it under the terms of the GNU Lesser General Public
*     License as published by the Free Software Foundation, either
*     version 3 of the License, or (at your option) any later
*     version.
*
*     This program is distributed in the hope that it will be useful,
*     but WITHOUT ANY WARRANTY; without even the implied warranty of
*     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*     GNU Lesser General Public License for more details.
*
*     You should have received a copy of the GNU Lesser General
*     License along with this program.  If not, see
*     <http://www.gnu.org/licenses/>.

*  Bugs:
*     {note_any_bugs_here}
*-
*/

#include "pal.h"
#include "palmac.h"
#include "pal1sofa.h"

void palEvp( double date, double deqx, double dvb[3], double dpb[3],
             double dvh[3], double dph[3] ){

/* Local Variables; */
   int i;
   double pvh[2][3], pvb[2][3], d1, d2, r[3][3];

/* BCRS PV-vectors. */
   eraEpv00 ( 2400000.5, date, pvh, pvb );

/* Was precession to another equinox requested? */
   if ( deqx > 0.0 ) {

/* Yes: compute precession matrix from J2000.0 to deqx. */
      eraEpj2jd ( deqx, &d1, &d2 );
      eraPmat06 ( d1, d2, r );

/* Rotate the PV-vectors. */
      eraRxpv ( r, pvh, pvh );
      eraRxpv ( r, pvb, pvb );
   }

/* Return the required vectors. */
   for ( i = 0; i < 3; i++ ) {
      dvh[i] = pvh[1][i] / PAL__SPD;
      dvb[i] = pvb[1][i] / PAL__SPD;
      dph[i] = pvh[0][i];
      dpb[i] = pvb[0][i];
   }
}