| 1 | /*
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| 2 | *+
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| 3 | * Name:
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| 4 | * palPrec
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| 5 |
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| 6 | * Purpose:
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| 7 | * Form the matrix of precession between two epochs (IAU 2006)
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| 8 |
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| 9 | * Language:
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| 10 | * Starlink ANSI C
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| 11 |
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| 12 | * Type of Module:
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| 13 | * Library routine
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| 14 |
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| 15 | * Invocation:
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| 16 | * palPrec( double ep0, double ep1, double rmatp[3][3] )
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| 17 |
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| 18 | * Arguments:
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| 19 | * ep0 = double (Given)
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| 20 | * Beginning epoch
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| 21 | * ep1 = double (Given)
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| 22 | * Ending epoch
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| 23 | * rmatp = double[3][3] (Returned)
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| 24 | * Precession matrix
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| 25 |
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| 26 | * Description:
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| 27 | * The IAU 2006 precession matrix from ep0 to ep1 is found and
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| 28 | * returned. The matrix is in the sense V(EP1) = RMATP * V(EP0).
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| 29 | * The epochs are TDB (loosely TT) Julian epochs.
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| 30 | *
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| 31 | * Though the matrix method itself is rigorous, the precession
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| 32 | * angles are expressed through canonical polynomials which are
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| 33 | * valid only for a limited time span of a few hundred years around
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| 34 | * the current epoch.
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| 35 |
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| 36 | * Authors:
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| 37 | * PTW: Pat Wallace (STFC)
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| 38 | * DSB: David Berry (JAC, Hawaii)
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| 39 | * {enter_new_authors_here}
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| 40 |
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| 41 | * History:
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| 42 | * 2012-02-10 (DSB):
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| 43 | * Initial version with documentation taken from Fortran SLA
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| 44 | * Adapted with permission from the Fortran SLALIB library.
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| 45 | * {enter_further_changes_here}
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| 46 |
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| 47 | * Copyright:
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| 48 | * Copyright (C) 1996 Rutherford Appleton Laboratory
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| 49 | * Copyright (C) 2012 Science and Technology Facilities Council.
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| 50 | * All Rights Reserved.
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| 51 |
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| 52 | * Licence:
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| 53 | * This program is free software: you can redistribute it and/or
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| 54 | * modify it under the terms of the GNU Lesser General Public
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| 55 | * License as published by the Free Software Foundation, either
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| 56 | * version 3 of the License, or (at your option) any later
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| 57 | * version.
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| 58 | *
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| 59 | * This program is distributed in the hope that it will be useful,
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| 60 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 61 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 62 | * GNU Lesser General Public License for more details.
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| 63 | *
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| 64 | * You should have received a copy of the GNU Lesser General
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| 65 | * License along with this program. If not, see
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| 66 | * <http://www.gnu.org/licenses/>.
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| 67 |
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| 68 | * Bugs:
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| 69 | * {note_any_bugs_here}
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| 70 | *-
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| 71 | */
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| 72 |
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| 73 | #include "pal.h"
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| 74 | #include "pal1sofa.h"
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| 75 |
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| 76 | void palPrec( double ep0, double ep1, double rmatp[3][3] ){
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| 77 |
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| 78 | /* Local Variables: */
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| 79 | double rmatq[3][3];
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| 80 | double ep0_days;
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| 81 | double ep1_days;
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| 82 |
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| 83 | /* Convert supplied dates to days since J2000 */
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| 84 | ep0_days = ( ep0 - 2000.0 )*ERFA_DJY;
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| 85 | ep1_days = ( ep1 - 2000.0 )*ERFA_DJY;
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| 86 |
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| 87 | /* If beginning epoch is J2000, just return the rotation matrix from
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| 88 | J2000 to EP1. */
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| 89 | if( ep0 == 2000.0 ) {
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| 90 | eraPmat06( ERFA_DJ00, ep1_days, rmatp );
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| 91 |
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| 92 | /* If end epoch is J2000, get the rotation matrix from J2000 to EP0 and
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| 93 | then transpose it to get the rotation matrix from EP0 to J2000. */
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| 94 | } else if( ep1 == 2000.0 ) {
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| 95 | eraPmat06( ERFA_DJ00, ep0_days, rmatp );
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| 96 | eraTr( rmatp, rmatp );
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| 97 |
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| 98 | /* Otherwise. get the two matrices used above and multiply them
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| 99 | together. */
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| 100 | } else {
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| 101 | eraPmat06( ERFA_DJ00, ep0_days, rmatp );
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| 102 | eraTr( rmatp, rmatp );
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| 103 | eraPmat06( ERFA_DJ00, ep1_days, rmatq );
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| 104 | eraRxr( rmatp, rmatq, rmatp );
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| 105 | }
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| 106 |
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| 107 | }
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