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/*
*+
* Name:
* palPrec
* Purpose:
* Form the matrix of precession between two epochs (IAU 2006)
* Language:
* Starlink ANSI C
* Type of Module:
* Library routine
* Invocation:
* palPrec( double ep0, double ep1, double rmatp[3][3] )
* Arguments:
* ep0 = double (Given)
* Beginning epoch
* ep1 = double (Given)
* Ending epoch
* rmatp = double[3][3] (Returned)
* Precession matrix
* Description:
* The IAU 2006 precession matrix from ep0 to ep1 is found and
* returned. The matrix is in the sense V(EP1) = RMATP * V(EP0).
* The epochs are TDB (loosely TT) Julian epochs.
*
* Though the matrix method itself is rigorous, the precession
* angles are expressed through canonical polynomials which are
* valid only for a limited time span of a few hundred years around
* the current epoch.
* Authors:
* PTW: Pat Wallace (STFC)
* DSB: David Berry (JAC, Hawaii)
* {enter_new_authors_here}
* History:
* 2012-02-10 (DSB):
* Initial version with documentation taken from Fortran SLA
* Adapted with permission from the Fortran SLALIB library.
* {enter_further_changes_here}
* Copyright:
* Copyright (C) 1996 Rutherford Appleton Laboratory
* 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 "pal1sofa.h"
void palPrec( double ep0, double ep1, double rmatp[3][3] ){
/* Local Variables: */
double rmatq[3][3];
double ep0_days;
double ep1_days;
/* Convert supplied dates to days since J2000 */
ep0_days = ( ep0 - 2000.0 )*ERFA_DJY;
ep1_days = ( ep1 - 2000.0 )*ERFA_DJY;
/* If beginning epoch is J2000, just return the rotation matrix from
J2000 to EP1. */
if( ep0 == 2000.0 ) {
eraPmat06( ERFA_DJ00, ep1_days, rmatp );
/* If end epoch is J2000, get the rotation matrix from J2000 to EP0 and
then transpose it to get the rotation matrix from EP0 to J2000. */
} else if( ep1 == 2000.0 ) {
eraPmat06( ERFA_DJ00, ep0_days, rmatp );
eraTr( rmatp, rmatp );
/* Otherwise. get the two matrices used above and multiply them
together. */
} else {
eraPmat06( ERFA_DJ00, ep0_days, rmatp );
eraTr( rmatp, rmatp );
eraPmat06( ERFA_DJ00, ep1_days, rmatq );
eraRxr( rmatp, rmatq, rmatp );
}
}
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