SUBROUTINE sla_PRECES (SYSTEM, EP0, EP1, RA, DC) *+ * - - - - - - - * P R E C E S * - - - - - - - * * Precession - either FK4 (Bessel-Newcomb, pre IAU 1976) or * FK5 (Fricke, post IAU 1976) as required. * * Given: * SYSTEM char precession to be applied: 'FK4' or 'FK5' * EP0,EP1 dp starting and ending epoch * RA,DC dp RA,Dec, mean equator & equinox of epoch EP0 * * Returned: * RA,DC dp RA,Dec, mean equator & equinox of epoch EP1 * * Called: sla_DRANRM, sla_PREBN, sla_PREC, sla_DCS2C, * sla_DMXV, sla_DCC2S * * Notes: * * 1) Lowercase characters in SYSTEM are acceptable. * * 2) The epochs are Besselian if SYSTEM='FK4' and Julian if 'FK5'. * For example, to precess coordinates in the old system from * equinox 1900.0 to 1950.0 the call would be: * CALL sla_PRECES ('FK4', 1900D0, 1950D0, RA, DC) * * 3) This routine will NOT correctly convert between the old and * the new systems - for example conversion from B1950 to J2000. * For these purposes see sla_FK425, sla_FK524, sla_FK45Z and * sla_FK54Z. * * 4) If an invalid SYSTEM is supplied, values of -99D0,-99D0 will * be returned for both RA and DC. * * P.T.Wallace Starlink 20 April 1990 * * Copyright (C) 1995 Rutherford Appleton Laboratory * * License: * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 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 General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program (see SLA_CONDITIONS); if not, write to the * Free Software Foundation, Inc., 59 Temple Place, Suite 330, * Boston, MA 02111-1307 USA * *- IMPLICIT NONE CHARACTER SYSTEM*(*) DOUBLE PRECISION EP0,EP1,RA,DC DOUBLE PRECISION PM(3,3),V1(3),V2(3) CHARACTER SYSUC*3 DOUBLE PRECISION sla_DRANRM * Convert to uppercase and validate SYSTEM SYSUC=SYSTEM IF (SYSUC(1:1).EQ.'f') SYSUC(1:1)='F' IF (SYSUC(2:2).EQ.'k') SYSUC(2:2)='K' IF (SYSUC.NE.'FK4'.AND.SYSUC.NE.'FK5') THEN RA=-99D0 DC=-99D0 ELSE * Generate appropriate precession matrix IF (SYSUC.EQ.'FK4') THEN CALL sla_PREBN(EP0,EP1,PM) ELSE CALL sla_PREC(EP0,EP1,PM) END IF * Convert RA,Dec to x,y,z CALL sla_DCS2C(RA,DC,V1) * Precess CALL sla_DMXV(PM,V1,V2) * Back to RA,Dec CALL sla_DCC2S(V2,RA,DC) RA=sla_DRANRM(RA) END IF END