| 1 | /*
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| 2 | *+
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| 3 | * Name:
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| 4 | * palPreces
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| 5 |
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| 6 | * Purpose:
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| 7 | * Precession - either FK4 or FK5 as required.
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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 | * void palPreces ( const char sys[3], double ep0, double ep1,
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| 17 | * double *ra, double *dc );
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| 18 |
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| 19 | * Arguments:
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| 20 | * sys = const char [3] (Given)
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| 21 | * Precession to be applied: FK4 or FK5. Case insensitive.
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| 22 | * ep0 = double (Given)
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| 23 | * Starting epoch.
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| 24 | * ep1 = double (Given)
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| 25 | * Ending epoch
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| 26 | * ra = double * (Given & Returned)
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| 27 | * On input the RA mean equator & equinox at epoch ep0. On exit
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| 28 | * the RA mean equator & equinox of epoch ep1.
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| 29 | * dec = double * (Given & Returned)
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| 30 | * On input the dec mean equator & equinox at epoch ep0. On exit
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| 31 | * the dec mean equator & equinox of epoch ep1.
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| 32 |
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| 33 | * Description:
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| 34 | * Precess coordinates using the appropriate system and epochs.
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| 35 |
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| 36 | * Authors:
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| 37 | * PTW: Patrick T. Wallace
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| 38 | * TIMJ: Tim Jenness (JAC, Hawaii)
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| 39 | * {enter_new_authors_here}
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| 40 |
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| 41 | * Notes:
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| 42 | * - Uses palPrec for FK5 data and palPrebn for FK4 data.
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| 43 | * - The epochs are Besselian if SYSTEM='FK4' and Julian if 'FK5'.
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| 44 | * For example, to precess coordinates in the old system from
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| 45 | * equinox 1900.0 to 1950.0 the call would be:
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| 46 | * palPreces( "FK4", 1900.0, 1950.0, &ra, &dc );
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| 47 | * - This routine will NOT correctly convert between the old and
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| 48 | * the new systems - for example conversion from B1950 to J2000.
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| 49 | * For these purposes see palFk425, palFk524, palFk45z and
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| 50 | * palFk54z.
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| 51 | * - If an invalid SYSTEM is supplied, values of -99D0,-99D0 will
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| 52 | * be returned for both RA and DC.
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| 53 |
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| 54 | * History:
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| 55 | * 2012-03-02 (TIMJ):
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| 56 | * Initial version
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| 57 | * Adapted with permission from the Fortran SLALIB library.
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| 58 | * {enter_further_changes_here}
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| 59 |
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| 60 | * Copyright:
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| 61 | * Copyright (C) 1995 Rutherford Appleton Laboratory
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| 62 | * Copyright (C) 2012 Science and Technology Facilities Council.
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| 63 | * All Rights Reserved.
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| 64 |
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| 65 | * Licence:
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| 66 | * This program is free software; you can redistribute it and/or
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| 67 | * modify it under the terms of the GNU General Public License as
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| 68 | * published by the Free Software Foundation; either version 3 of
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| 69 | * the License, or (at your option) any later version.
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| 70 | *
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| 71 | * This program is distributed in the hope that it will be
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| 72 | * useful, but WITHOUT ANY WARRANTY; without even the implied
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| 73 | * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
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| 74 | * PURPOSE. See the GNU General Public License for more details.
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| 75 | *
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| 76 | * You should have received a copy of the GNU General Public License
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| 77 | * along with this program; if not, write to the Free Software
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| 78 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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| 79 | * MA 02110-1301, USA.
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| 80 |
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| 81 | * Bugs:
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| 82 | * {note_any_bugs_here}
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| 83 | *-
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| 84 | */
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| 85 |
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| 86 | #include "pal.h"
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| 87 | #include "pal1sofa.h"
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| 88 |
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| 89 | #include <string.h>
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| 90 |
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| 91 | void palPreces ( const char sys[3], double ep0, double ep1,
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| 92 | double *ra, double *dc ) {
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| 93 |
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| 94 | double pm[3][3];
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| 95 | double v1[3];
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| 96 | double v2[3];
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| 97 |
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| 98 | /* Generate appropriate precession matrix */
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| 99 | if ( strncasecmp( "FK4", sys, 3 ) == 0 ) {
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| 100 | palPrebn( ep0, ep1, pm );
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| 101 | } else if (strncasecmp( "FK5", sys, 3 ) == 0 ) {
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| 102 | palPrec( ep0, ep1, pm );
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| 103 | } else {
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| 104 | *ra = -99.0;
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| 105 | *dc = -99.0;
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| 106 | return;
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| 107 | }
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| 108 |
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| 109 | /* Convert RA,Dec to x,y,z */
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| 110 | eraS2c( *ra, *dc, v1 );
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| 111 |
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| 112 | /* Precess */
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| 113 | eraRxp( pm, v1, v2 );
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| 114 |
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| 115 | /* Back to RA,Dec */
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| 116 | eraC2s( v2, ra, dc );
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| 117 | *ra = eraAnp( *ra );
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| 118 | }
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