| 1 | /*
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| 2 | *+
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| 3 | * Name:
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| 4 | * palFk54z
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| 5 |
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| 6 | * Purpose:
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| 7 | * Convert a J2000.0 FK5 star position to B1950.0 FK4 assuming
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| 8 | * zero proper motion and parallax.
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| 9 |
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| 10 | * Language:
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| 11 | * Starlink ANSI C
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| 12 |
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| 13 | * Type of Module:
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| 14 | * Library routine
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| 15 |
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| 16 | * Invocation:
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| 17 | * palFk54z( double r2000, double d2000, double bepoch, double *r1950,
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| 18 | * double *d1950, double *dr1950, double *dd1950 )
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| 19 |
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| 20 | * Arguments:
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| 21 | * r2000 = double (Given)
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| 22 | * J2000.0 FK5 RA (radians).
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| 23 | * d2000 = double (Given)
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| 24 | * J2000.0 FK5 Dec (radians).
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| 25 | * bepoch = double (Given)
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| 26 | * Besselian epoch (e.g. 1950.0).
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| 27 | * r1950 = double * (Returned)
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| 28 | * B1950 FK4 RA (radians) at epoch "bepoch".
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| 29 | * d1950 = double * (Returned)
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| 30 | * B1950 FK4 Dec (radians) at epoch "bepoch".
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| 31 | * dr1950 = double * (Returned)
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| 32 | * B1950 FK4 proper motion (RA) (radians/trop.yr)).
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| 33 | * dr1950 = double * (Returned)
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| 34 | * B1950 FK4 proper motion (Dec) (radians/trop.yr)).
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| 35 |
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| 36 | * Description:
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| 37 | * This function converts star positions from the IAU 1976,
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| 38 | * FK5, Fricke system to the Bessel-Newcomb, FK4 system.
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| 39 |
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| 40 | * Notes:
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| 41 | * - The proper motion in RA is dRA/dt rather than cos(Dec)*dRA/dt.
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| 42 | * - Conversion from Julian epoch 2000.0 to Besselian epoch 1950.0
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| 43 | * only is provided for. Conversions involving other epochs will
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| 44 | * require use of the appropriate precession functions before and
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| 45 | * after this function is called.
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| 46 | * - The FK5 proper motions, the parallax and the radial velocity
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| 47 | * are presumed zero.
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| 48 | * - It is the intention that FK5 should be a close approximation
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| 49 | * to an inertial frame, so that distant objects have zero proper
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| 50 | * motion; such objects have (in general) non-zero proper motion
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| 51 | * in FK4, and this function returns those fictitious proper
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| 52 | * motions.
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| 53 | * - The position returned by this function is in the B1950
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| 54 | * reference frame but at Besselian epoch BEPOCH. For comparison
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| 55 | * with catalogues the "bepoch" argument will frequently be 1950.0.
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| 56 |
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| 57 | * Authors:
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| 58 | * PTW: Pat Wallace (STFC)
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| 59 | * DSB: David Berry (JAC, Hawaii)
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| 60 | * {enter_new_authors_here}
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| 61 |
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| 62 | * History:
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| 63 | * 2012-02-13 (DSB):
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| 64 | * Initial version with documentation taken from Fortran SLA
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| 65 | * Adapted with permission from the Fortran SLALIB library.
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| 66 | * {enter_further_changes_here}
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| 67 |
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| 68 | * Copyright:
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| 69 | * Copyright (C) 1995 Rutherford Appleton Laboratory
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| 70 | * Copyright (C) 2012 Science and Technology Facilities Council.
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| 71 | * All Rights Reserved.
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| 72 |
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| 73 | * Licence:
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| 74 | * This program is free software: you can redistribute it and/or
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| 75 | * modify it under the terms of the GNU Lesser General Public
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| 76 | * License as published by the Free Software Foundation, either
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| 77 | * version 3 of the License, or (at your option) any later
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| 78 | * version.
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| 79 | *
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| 80 | * This program is distributed in the hope that it will be useful,
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| 81 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 82 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 83 | * GNU Lesser General Public License for more details.
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| 84 | *
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| 85 | * You should have received a copy of the GNU Lesser General
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| 86 | * License along with this program. If not, see
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| 87 | * <http://www.gnu.org/licenses/>.
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| 88 |
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| 89 | * Bugs:
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| 90 | * {note_any_bugs_here}
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| 91 | *-
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| 92 | */
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| 93 |
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| 94 | #include "pal.h"
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| 95 | #include "pal1sofa.h"
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| 96 |
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| 97 | void palFk54z( double r2000, double d2000, double bepoch, double *r1950,
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| 98 | double *d1950, double *dr1950, double *dd1950 ){
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| 99 |
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| 100 | /* Local Variables: */
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| 101 | double r, d, px, rv, y;
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| 102 |
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| 103 | /* FK5 equinox J2000 (any epoch) to FK4 equinox B1950 epoch B1950. */
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| 104 | palFk524( r2000, d2000, 0.0, 0.0, 0.0, 0.0, &r, &d, dr1950, dd1950,
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| 105 | &px, &rv );
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| 106 |
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| 107 | /* Fictitious proper motion to epoch "bepoch". */
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| 108 | y = bepoch - 1950.0;
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| 109 | *r1950 = r + *dr1950*y;
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| 110 | *d1950 = d + *dd1950*y;
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| 111 |
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| 112 | }
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| 113 |
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