source: trunk/FACT++/erfa/src/tttdb.c@ 18403

Last change on this file since 18403 was 18348, checked in by tbretz, 9 years ago
File size: 4.8 KB
Line 
1#include "erfa.h"
2
3int eraTttdb(double tt1, double tt2, double dtr,
4 double *tdb1, double *tdb2)
5/*
6** - - - - - - - - -
7** e r a T t t d b
8** - - - - - - - - -
9**
10** Time scale transformation: Terrestrial Time, TT, to Barycentric
11** Dynamical Time, TDB.
12**
13** Given:
14** tt1,tt2 double TT as a 2-part Julian Date
15** dtr double TDB-TT in seconds
16**
17** Returned:
18** tdb1,tdb2 double TDB as a 2-part Julian Date
19**
20** Returned (function value):
21** int status: 0 = OK
22**
23** Notes:
24**
25** 1) tt1+tt2 is Julian Date, apportioned in any convenient way between
26** the two arguments, for example where tt1 is the Julian Day Number
27** and tt2 is the fraction of a day. The returned tdb1,tdb2 follow
28** suit.
29**
30** 2) The argument dtr represents the quasi-periodic component of the
31** GR transformation between TT and TCB. It is dependent upon the
32** adopted solar-system ephemeris, and can be obtained by numerical
33** integration, by interrogating a precomputed time ephemeris or by
34** evaluating a model such as that implemented in the ERFA function
35** eraDtdb. The quantity is dominated by an annual term of 1.7 ms
36** amplitude.
37**
38** 3) TDB is essentially the same as Teph, the time argument for the JPL
39** solar system ephemerides.
40**
41** References:
42**
43** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
44** IERS Technical Note No. 32, BKG (2004)
45**
46** IAU 2006 Resolution 3
47**
48** Copyright (C) 2013-2015, NumFOCUS Foundation.
49** Derived, with permission, from the SOFA library. See notes at end of file.
50*/
51{
52 double dtrd;
53
54/* Result, safeguarding precision. */
55 dtrd = dtr / ERFA_DAYSEC;
56 if ( tt1 > tt2 ) {
57 *tdb1 = tt1;
58 *tdb2 = tt2 + dtrd;
59 } else {
60 *tdb1 = tt1 + dtrd;
61 *tdb2 = tt2;
62 }
63
64/* Status (always OK). */
65 return 0;
66
67}
68/*----------------------------------------------------------------------
69**
70**
71** Copyright (C) 2013-2015, NumFOCUS Foundation.
72** All rights reserved.
73**
74** This library is derived, with permission, from the International
75** Astronomical Union's "Standards of Fundamental Astronomy" library,
76** available from http://www.iausofa.org.
77**
78** The ERFA version is intended to retain identical functionality to
79** the SOFA library, but made distinct through different function and
80** file names, as set out in the SOFA license conditions. The SOFA
81** original has a role as a reference standard for the IAU and IERS,
82** and consequently redistribution is permitted only in its unaltered
83** state. The ERFA version is not subject to this restriction and
84** therefore can be included in distributions which do not support the
85** concept of "read only" software.
86**
87** Although the intent is to replicate the SOFA API (other than
88** replacement of prefix names) and results (with the exception of
89** bugs; any that are discovered will be fixed), SOFA is not
90** responsible for any errors found in this version of the library.
91**
92** If you wish to acknowledge the SOFA heritage, please acknowledge
93** that you are using a library derived from SOFA, rather than SOFA
94** itself.
95**
96**
97** TERMS AND CONDITIONS
98**
99** Redistribution and use in source and binary forms, with or without
100** modification, are permitted provided that the following conditions
101** are met:
102**
103** 1 Redistributions of source code must retain the above copyright
104** notice, this list of conditions and the following disclaimer.
105**
106** 2 Redistributions in binary form must reproduce the above copyright
107** notice, this list of conditions and the following disclaimer in
108** the documentation and/or other materials provided with the
109** distribution.
110**
111** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
112** the International Astronomical Union nor the names of its
113** contributors may be used to endorse or promote products derived
114** from this software without specific prior written permission.
115**
116** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
117** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
118** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
119** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
120** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
121** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
122** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
123** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
124** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
125** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
126** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
127** POSSIBILITY OF SUCH DAMAGE.
128**
129*/
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