1 #include "erfa.h"
2 #include "erfam.h"
3
eraTttdb(double tt1,double tt2,double dtr,double * tdb1,double * tdb2)4 int eraTttdb(double tt1, double tt2, double dtr,
5 double *tdb1, double *tdb2)
6 /*
7 ** - - - - - - - - -
8 ** e r a T t t d b
9 ** - - - - - - - - -
10 **
11 ** Time scale transformation: Terrestrial Time, TT, to Barycentric
12 ** Dynamical Time, TDB.
13 **
14 ** Given:
15 ** tt1,tt2 double TT as a 2-part Julian Date
16 ** dtr double TDB-TT in seconds
17 **
18 ** Returned:
19 ** tdb1,tdb2 double TDB as a 2-part Julian Date
20 **
21 ** Returned (function value):
22 ** int status: 0 = OK
23 **
24 ** Notes:
25 **
26 ** 1) tt1+tt2 is Julian Date, apportioned in any convenient way between
27 ** the two arguments, for example where tt1 is the Julian Day Number
28 ** and tt2 is the fraction of a day. The returned tdb1,tdb2 follow
29 ** suit.
30 **
31 ** 2) The argument dtr represents the quasi-periodic component of the
32 ** GR transformation between TT and TCB. It is dependent upon the
33 ** adopted solar-system ephemeris, and can be obtained by numerical
34 ** integration, by interrogating a precomputed time ephemeris or by
35 ** evaluating a model such as that implemented in the ERFA function
36 ** eraDtdb. The quantity is dominated by an annual term of 1.7 ms
37 ** amplitude.
38 **
39 ** 3) TDB is essentially the same as Teph, the time argument for the JPL
40 ** solar system ephemerides.
41 **
42 ** References:
43 **
44 ** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
45 ** IERS Technical Note No. 32, BKG (2004)
46 **
47 ** IAU 2006 Resolution 3
48 **
49 ** This revision: 2021 May 11
50 **
51 ** Copyright (C) 2013-2021, NumFOCUS Foundation.
52 ** Derived, with permission, from the SOFA library. See notes at end of file.
53 */
54 {
55 double dtrd;
56
57
58 /* Result, safeguarding precision. */
59 dtrd = dtr / ERFA_DAYSEC;
60 if ( fabs(tt1) > fabs(tt2) ) {
61 *tdb1 = tt1;
62 *tdb2 = tt2 + dtrd;
63 } else {
64 *tdb1 = tt1 + dtrd;
65 *tdb2 = tt2;
66 }
67
68 /* Status (always OK). */
69 return 0;
70
71 /* Finished. */
72
73 }
74 /*----------------------------------------------------------------------
75 **
76 **
77 ** Copyright (C) 2013-2021, NumFOCUS Foundation.
78 ** All rights reserved.
79 **
80 ** This library is derived, with permission, from the International
81 ** Astronomical Union's "Standards of Fundamental Astronomy" library,
82 ** available from http://www.iausofa.org.
83 **
84 ** The ERFA version is intended to retain identical functionality to
85 ** the SOFA library, but made distinct through different function and
86 ** file names, as set out in the SOFA license conditions. The SOFA
87 ** original has a role as a reference standard for the IAU and IERS,
88 ** and consequently redistribution is permitted only in its unaltered
89 ** state. The ERFA version is not subject to this restriction and
90 ** therefore can be included in distributions which do not support the
91 ** concept of "read only" software.
92 **
93 ** Although the intent is to replicate the SOFA API (other than
94 ** replacement of prefix names) and results (with the exception of
95 ** bugs; any that are discovered will be fixed), SOFA is not
96 ** responsible for any errors found in this version of the library.
97 **
98 ** If you wish to acknowledge the SOFA heritage, please acknowledge
99 ** that you are using a library derived from SOFA, rather than SOFA
100 ** itself.
101 **
102 **
103 ** TERMS AND CONDITIONS
104 **
105 ** Redistribution and use in source and binary forms, with or without
106 ** modification, are permitted provided that the following conditions
107 ** are met:
108 **
109 ** 1 Redistributions of source code must retain the above copyright
110 ** notice, this list of conditions and the following disclaimer.
111 **
112 ** 2 Redistributions in binary form must reproduce the above copyright
113 ** notice, this list of conditions and the following disclaimer in
114 ** the documentation and/or other materials provided with the
115 ** distribution.
116 **
117 ** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
118 ** the International Astronomical Union nor the names of its
119 ** contributors may be used to endorse or promote products derived
120 ** from this software without specific prior written permission.
121 **
122 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
123 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
124 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
125 ** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
126 ** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
127 ** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
128 ** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
129 ** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
130 ** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
131 ** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
132 ** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
133 ** POSSIBILITY OF SUCH DAMAGE.
134 **
135 */
136