1 /* 2 * - - - - - - - - - 3 * g a l _ s p 0 0 4 * - - - - - - - - - 5 * 6 * This routine is part of the General Astrodynamics Library 7 * 8 * Description: 9 * 10 * The TIO locator s', positioning the Terrestrial Intermediate Origin 11 * on the equator of the Celestial Intermediate Pole. 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 * canonical model. 19 * 20 * Given: 21 * 22 * date1,date2 d TT as a 2-part Julian Date (Note 1) 23 * 24 * Returned: 25 * 26 * gal_sp00 d the TIO locator s' in radians (Note 2) 27 * 28 * Notes: 29 * 30 * 1) The TT date date1+date2 is a Julian Date, apportioned in any 31 * convenient way between the two arguments. For example, 32 * JD(TT)=2450123.7 could be expressed in any of these ways, 33 * among others: 34 * 35 * date1 date2 36 * 37 * 2450123.7 0.0 (JD method) 38 * 2451545.0 -1421.3 (J2000 method) 39 * 2400000.5 50123.2 (MJD method) 40 * 2450123.5 0.2 (date & time method) 41 * 42 * The JD method is the most natural and convenient to use in 43 * cases where the loss of several decimal digits of resolution 44 * is acceptable. The J2000 method is best matched to the way 45 * the argument is handled internally and will deliver the 46 * optimum resolution. The MJD method and the date & time methods 47 * are both good compromises between resolution and convenience. 48 * 49 * 2) The TIO locator s' is obtained from polar motion observations by 50 * numerical integration, and so is in essence unpredictable. 51 * However, it is dominated by a secular drift of about 52 * 47 microarcseconds per century, which is the approximation 53 * evaluated by the present routine. 54 * 55 * References: 56 * 57 * McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), 58 * IERS Technical Note No. 32, BKG (2004) 59 * 60 * This revision: 61 * 62 * 2006 October 10 ( c version 2008 January 19 ) 63 * 64 * 65 * Copyright (C) 2008 Paul C. L. Willmott. See notes at end. 66 * 67 *----------------------------------------------------------------------- 68 */ 69 70 #ifndef _GAL_SP00_H_ 71 #define _GAL_SP00_H_ 1 72 73 #undef __BEGIN_DECLS 74 #undef __END_DECLS 75 #ifdef __cplusplus 76 #define __BEGIN_DECLS extern "C" { 77 #define __END_DECLS } 78 #else 79 #define __BEGIN_DECLS /* empty */ 80 #define __END_DECLS /* empty */ 81 #endif 82 83 __BEGIN_DECLS 84 85 double 86 gal_sp00 87 ( 88 double date1, 89 double date2 90 ) ; 91 92 __END_DECLS 93 94 #endif /* !_GAL_SP00_H_ */ 95 96 /* 97 * gal - General Astrodynamics Library 98 * Copyright (C) 2008 Paul C. L. Willmott 99 * 100 * This program is free software; you can redistribute it and/or modify 101 * it under the terms of the GNU General Public License as published by 102 * the Free Software Foundation; either version 2 of the License, or 103 * (at your option) any later version. 104 * 105 * This program is distributed in the hope that it will be useful, 106 * but WITHOUT ANY WARRANTY; without even the implied warranty of 107 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 108 * GNU General Public License for more details. 109 * 110 * You should have received a copy of the GNU General Public License along 111 * with this program; if not, write to the Free Software Foundation, Inc., 112 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. 113 * 114 * Contact: 115 * 116 * Paul Willmott 117 * vp9mu@amsat.org 118 */ 119