| 1 | #include "slalib.h"
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| 2 | #include "slamac.h"
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| 3 | #include <ctype.h>
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| 4 | void slaPreces ( char sys[3], double ep0, double ep1,
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| 5 | double *ra, double *dc )
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| 6 | /*
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| 7 | ** - - - - - - - - - -
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| 8 | ** s l a P r e c e s
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| 9 | ** - - - - - - - - - -
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| 10 | **
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| 11 | ** Precession - either FK4 (Bessel-Newcomb, pre-IAU1976) or
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| 12 | ** FK5 (Fricke, post-IAU1976) as required.
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| 13 | **
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| 14 | ** Given:
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| 15 | ** sys char[] precession to be applied: "FK4" or "FK5"
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| 16 | ** ep0,ep1 double starting and ending epoch
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| 17 | ** ra,dc double RA,Dec, mean equator & equinox of epoch ep0
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| 18 | **
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| 19 | ** Returned:
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| 20 | ** *ra,*dc double RA,Dec, mean equator & equinox of epoch ep1
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| 21 | **
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| 22 | ** Called: slaDranrm, slaPrebn, slaPrec, slaDcs2c,
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| 23 | ** slaDmxv, slaDcc2s
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| 24 | **
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| 25 | ** Notes:
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| 26 | **
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| 27 | ** 1) The epochs are Besselian if sys='FK4' and Julian if 'FK5'.
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| 28 | ** For example, to precess coordinates in the old system from
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| 29 | ** equinox 1900.0 to 1950.0 the call would be:
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| 30 | ** slaPreces ( "FK4", 1900.0, 1950.0, &ra, &dc )
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| 31 | **
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| 32 | ** 2) This routine will not correctly convert between the old and
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| 33 | ** the new systems - for example conversion from B1950 to J2000.
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| 34 | ** For these purposes see slaFk425, slaFk524, slaFk45z and
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| 35 | ** slaFk54z.
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| 36 | **
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| 37 | ** 3) If an invalid sys is supplied, values of -99.0,-99.0 will
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| 38 | ** be returned for both ra and dc.
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| 39 | **
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| 40 | ** Last revision: 22 December 1993
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| 41 | **
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| 42 | ** Copyright P.T.Wallace. All rights reserved.
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| 43 | */
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| 44 | {
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| 45 | double pm[3][3], v1[3], v2[3];
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| 46 |
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| 47 | /* Validate sys */
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| 48 | if ( ( toupper ( sys[0] ) != 'F' )
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| 49 | || ( toupper ( sys[1] ) != 'K' )
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| 50 | || ( sys[2] != '4' && sys[2] != '5' ) ) {
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| 51 | *ra = -99.0; /* Error */
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| 52 | *dc = -99.0;
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| 53 | } else {
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| 54 |
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| 55 | /* Generate appropriate precession matrix */
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| 56 | if ( sys[2] == '4' )
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| 57 | slaPrebn ( ep0, ep1, pm );
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| 58 | else
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| 59 | slaPrec ( ep0, ep1, pm );
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| 60 |
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| 61 | /* Convert RA,Dec to x,y,z */
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| 62 | slaDcs2c ( *ra, *dc, v1 );
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| 63 |
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| 64 | /* Precess */
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| 65 | slaDmxv ( pm, v1, v2 );
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| 66 |
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| 67 | /* Back to RA,Dec */
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| 68 | slaDcc2s ( v2, ra, dc );
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| 69 | *ra = slaDranrm ( *ra );
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| 70 | }
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| 71 | }
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