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