1 /* 2 * - - - - - - - - - - 3 * g a l _ f k 5 h z 4 * - - - - - - - - - - 5 * 6 * This routine is part of the General Astrodynamics Library 7 * 8 * Description: 9 * 10 * Transform an FK5 (J2000) star position into the system of the 11 * Hipparcos catalogue, assuming zero Hipparcos proper motion. 12 * 13 * This routine is an independent translation of a FORTRAN routine 14 * that is part of IAU's SOFA software collection. 15 * 16 * Status: 17 * 18 * support routine. 19 * 20 * Given: 21 * 22 * r5 d FK5 RA (radians), equinox J2000, at date 23 * d5 d FK5 Dec (radians), equinox J2000, at date 24 * date1,date2 d TDB date (Notes 1,2) 25 * 26 * Returned: 27 * 28 * *rh d Hipparcos RA (radians) 29 * *dh d Hipparcos Dec (radians) 30 * 31 * Notes: 32 * 33 * 1) This routine converts a star position from the FK5 system to 34 * the Hipparcos system, in such a way that the Hipparcos proper 35 * motion is zero. Because such a star has, in general, a non-zero 36 * proper motion in the FK5 system, the routine requires the date 37 * at which the position in the FK5 system was determined. 38 * 39 * 2) The TT date date1+date2 is a Julian Date, apportioned in any 40 * convenient way between the two arguments. For example, 41 * JD(TT)=2450123.7 could be expressed in any of these ways, 42 * among others: 43 * 44 * date1 date2 45 * 46 * 2450123.7 0.0 (JD method) 47 * 2451545.0 -1421.3 (J2000 method) 48 * 2400000.5 50123.2 (MJD method) 49 * 2450123.5 0.2 (date & time method) 50 * 51 * The JD method is the most natural and convenient to use in 52 * cases where the loss of several decimal digits of resolution 53 * is acceptable. The J2000 method is best matched to the way 54 * the argument is handled internally and will deliver the 55 * optimum resolution. The MJD method and the date & time methods 56 * are both good compromises between resolution and convenience. 57 * 58 * 3) The FK5 to Hipparcos transformation is modeled as a pure 59 * rotation and spin; zonal errors in the FK5 catalogue are 60 * not taken into account. 61 * 62 * 4) It was the intention that Hipparcos should be a close 63 * approximation to an inertial frame, so that distant objects 64 * have zero proper motion; such objects have (in general) 65 * non-zero proper motion in FK5, and this routine returns those 66 * fictitious proper motions. 67 * 68 * 5) The position returned by this routine is in the FK5 J2000 69 * reference system but at date date1+date2. 70 * 71 * 6) See also gal_fk52h, gal_h2fk5, gal_hfk5z. 72 * 73 * Called: 74 * 75 * gal_s2c spherical coordinates to unit vector 76 * gal_fk5hip FK5 to Hipparcos rotation and spin 77 * gal_sxp multiply p-vector by scalar 78 * gal_rv2m r-vector to r-matrix 79 * gal_trxp product of transpose of r-matrix and p-vector 80 * gal_pxp vector product of two p-vectors 81 * gal_c2s p-vector to spherical 82 * gal_anp normalize angle into range 0 to 2pi 83 * 84 * References: 85 * 86 * F.Mignard & M.Froeschle, Astron. Astrophys. 354, 732-739 (2000). 87 * 88 * This revision: 89 * 90 * 2007 April 18 ( c version 2008 February 4 ) 91 * 92 * 93 * Copyright (C) 2008 Paul C. L. Willmott. See notes at end. 94 * 95 *----------------------------------------------------------------------- 96 */ 97 98 #ifndef _GAL_FK5HZ_H_ 99 #define _GAL_FK5HZ_H_ 1 100 101 #undef __BEGIN_DECLS 102 #undef __END_DECLS 103 #ifdef __cplusplus 104 #define __BEGIN_DECLS extern "C" { 105 #define __END_DECLS } 106 #else 107 #define __BEGIN_DECLS /* empty */ 108 #define __END_DECLS /* empty */ 109 #endif 110 111 __BEGIN_DECLS 112 113 void 114 gal_fk5hz 115 ( 116 double r5, 117 double d5, 118 double date1, 119 double date2, 120 double *rh, 121 double *dh 122 ) ; 123 124 __END_DECLS 125 126 #endif /* !_GAL_FK5HZ_H_ */ 127 128 /* 129 * gal - General Astrodynamics Library 130 * Copyright (C) 2008 Paul C. L. Willmott 131 * 132 * This program is free software; you can redistribute it and/or modify 133 * it under the terms of the GNU General Public License as published by 134 * the Free Software Foundation; either version 2 of the License, or 135 * (at your option) any later version. 136 * 137 * This program is distributed in the hope that it will be useful, 138 * but WITHOUT ANY WARRANTY; without even the implied warranty of 139 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 140 * GNU General Public License for more details. 141 * 142 * You should have received a copy of the GNU General Public License along 143 * with this program; if not, write to the Free Software Foundation, Inc., 144 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. 145 * 146 * Contact: 147 * 148 * Paul Willmott 149 * vp9mu@amsat.org 150 */ 151