1 #include "erfa.h"
2
eraTttcg(double tt1,double tt2,double * tcg1,double * tcg2)3 int eraTttcg(double tt1, double tt2, double *tcg1, double *tcg2)
4 /*
5 ** - - - - - - - - -
6 ** e r a T t t c g
7 ** - - - - - - - - -
8 **
9 ** Time scale transformation: Terrestrial Time, TT, to Geocentric
10 ** Coordinate Time, TCG.
11 **
12 ** Given:
13 ** tt1,tt2 double TT as a 2-part Julian Date
14 **
15 ** Returned:
16 ** tcg1,tcg2 double TCG as a 2-part Julian Date
17 **
18 ** Returned (function value):
19 ** int status: 0 = OK
20 **
21 ** Note:
22 **
23 ** tt1+tt2 is Julian Date, apportioned in any convenient way between
24 ** the two arguments, for example where tt1 is the Julian Day Number
25 ** and tt2 is the fraction of a day. The returned tcg1,tcg2 follow
26 ** suit.
27 **
28 ** References:
29 **
30 ** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
31 ** IERS Technical Note No. 32, BKG (2004)
32 **
33 ** IAU 2000 Resolution B1.9
34 **
35 ** Copyright (C) 2013-2020, NumFOCUS Foundation.
36 ** Derived, with permission, from the SOFA library. See notes at end of file.
37 */
38 {
39
40 /* 1977 Jan 1 00:00:32.184 TT, as MJD */
41 static const double t77t = ERFA_DJM77 + ERFA_TTMTAI/ERFA_DAYSEC;
42
43 /* TT to TCG rate */
44 static const double elgg = ERFA_ELG/(1.0-ERFA_ELG);
45
46
47 /* Result, safeguarding precision. */
48 if ( fabs(tt1) > fabs(tt2) ) {
49 *tcg1 = tt1;
50 *tcg2 = tt2 + ( ( tt1 - ERFA_DJM0 ) + ( tt2 - t77t ) ) * elgg;
51 } else {
52 *tcg1 = tt1 + ( ( tt2 - ERFA_DJM0 ) + ( tt1 - t77t ) ) * elgg;
53 *tcg2 = tt2;
54 }
55
56 /* Status (always OK). */
57 return 0;
58
59 }
60 /*----------------------------------------------------------------------
61 **
62 **
63 ** Copyright (C) 2013-2020, NumFOCUS Foundation.
64 ** All rights reserved.
65 **
66 ** This library is derived, with permission, from the International
67 ** Astronomical Union's "Standards of Fundamental Astronomy" library,
68 ** available from http://www.iausofa.org.
69 **
70 ** The ERFA version is intended to retain identical functionality to
71 ** the SOFA library, but made distinct through different function and
72 ** file names, as set out in the SOFA license conditions. The SOFA
73 ** original has a role as a reference standard for the IAU and IERS,
74 ** and consequently redistribution is permitted only in its unaltered
75 ** state. The ERFA version is not subject to this restriction and
76 ** therefore can be included in distributions which do not support the
77 ** concept of "read only" software.
78 **
79 ** Although the intent is to replicate the SOFA API (other than
80 ** replacement of prefix names) and results (with the exception of
81 ** bugs; any that are discovered will be fixed), SOFA is not
82 ** responsible for any errors found in this version of the library.
83 **
84 ** If you wish to acknowledge the SOFA heritage, please acknowledge
85 ** that you are using a library derived from SOFA, rather than SOFA
86 ** itself.
87 **
88 **
89 ** TERMS AND CONDITIONS
90 **
91 ** Redistribution and use in source and binary forms, with or without
92 ** modification, are permitted provided that the following conditions
93 ** are met:
94 **
95 ** 1 Redistributions of source code must retain the above copyright
96 ** notice, this list of conditions and the following disclaimer.
97 **
98 ** 2 Redistributions in binary form must reproduce the above copyright
99 ** notice, this list of conditions and the following disclaimer in
100 ** the documentation and/or other materials provided with the
101 ** distribution.
102 **
103 ** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
104 ** the International Astronomical Union nor the names of its
105 ** contributors may be used to endorse or promote products derived
106 ** from this software without specific prior written permission.
107 **
108 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
109 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
110 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
111 ** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
112 ** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
113 ** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
114 ** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
115 ** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
116 ** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
117 ** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
118 ** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
119 ** POSSIBILITY OF SUCH DAMAGE.
120 **
121 */
122