source: trunk/FACT++/sofa/src/tdbtt.c@ 18368

Last change on this file since 18368 was 18346, checked in by tbretz, 11 years ago
File size: 6.2 KB
Line 
1#include "sofa.h"
2
3int iauTdbtt(double tdb1, double tdb2, double dtr,
4 double *tt1, double *tt2 )
5/*
6** - - - - - - - - -
7** i a u T d b t t
8** - - - - - - - - -
9**
10** Time scale transformation: Barycentric Dynamical Time, TDB, to
11** Terrestrial Time, TT.
12**
13** This function is part of the International Astronomical Union's
14** SOFA (Standards of Fundamental Astronomy) software collection.
15**
16** Status: canonical.
17**
18** Given:
19** tdb1,tdb2 double TDB as a 2-part Julian Date
20** dtr double TDB-TT in seconds
21**
22** Returned:
23** tt1,tt2 double TT as a 2-part Julian Date
24**
25** Returned (function value):
26** int status: 0 = OK
27**
28** Notes:
29**
30** 1) tdb1+tdb2 is Julian Date, apportioned in any convenient way
31** between the two arguments, for example where tdb1 is the Julian
32** Day Number and tdb2 is the fraction of a day. The returned
33** tt1,tt2 follow suit.
34**
35** 2) The argument dtr represents the quasi-periodic component of the
36** GR transformation between TT and TCB. It is dependent upon the
37** adopted solar-system ephemeris, and can be obtained by numerical
38** integration, by interrogating a precomputed time ephemeris or by
39** evaluating a model such as that implemented in the SOFA function
40** iauDtdb. The quantity is dominated by an annual term of 1.7 ms
41** amplitude.
42**
43** 3) TDB is essentially the same as Teph, the time argument for the
44** JPL solar system ephemerides.
45**
46** References:
47**
48** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
49** IERS Technical Note No. 32, BKG (2004)
50**
51** IAU 2006 Resolution 3
52**
53** This revision: 2013 June 18
54**
55** SOFA release 2015-02-09
56**
57** Copyright (C) 2015 IAU SOFA Board. See notes at end.
58**
59*/
60{
61 double dtrd;
62
63/* Result, safeguarding precision. */
64 dtrd = dtr / DAYSEC;
65 if ( tdb1 > tdb2 ) {
66 *tt1 = tdb1;
67 *tt2 = tdb2 - dtrd;
68 } else {
69 *tt1 = tdb1 - dtrd;
70 *tt2 = tdb2;
71 }
72
73/* Status (always OK). */
74 return 0;
75
76/*----------------------------------------------------------------------
77**
78** Copyright (C) 2015
79** Standards Of Fundamental Astronomy Board
80** of the International Astronomical Union.
81**
82** =====================
83** SOFA Software License
84** =====================
85**
86** NOTICE TO USER:
87**
88** BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
89** CONDITIONS WHICH APPLY TO ITS USE.
90**
91** 1. The Software is owned by the IAU SOFA Board ("SOFA").
92**
93** 2. Permission is granted to anyone to use the SOFA software for any
94** purpose, including commercial applications, free of charge and
95** without payment of royalties, subject to the conditions and
96** restrictions listed below.
97**
98** 3. You (the user) may copy and distribute SOFA source code to others,
99** and use and adapt its code and algorithms in your own software,
100** on a world-wide, royalty-free basis. That portion of your
101** distribution that does not consist of intact and unchanged copies
102** of SOFA source code files is a "derived work" that must comply
103** with the following requirements:
104**
105** a) Your work shall be marked or carry a statement that it
106** (i) uses routines and computations derived by you from
107** software provided by SOFA under license to you; and
108** (ii) does not itself constitute software provided by and/or
109** endorsed by SOFA.
110**
111** b) The source code of your derived work must contain descriptions
112** of how the derived work is based upon, contains and/or differs
113** from the original SOFA software.
114**
115** c) The names of all routines in your derived work shall not
116** include the prefix "iau" or "sofa" or trivial modifications
117** thereof such as changes of case.
118**
119** d) The origin of the SOFA components of your derived work must
120** not be misrepresented; you must not claim that you wrote the
121** original software, nor file a patent application for SOFA
122** software or algorithms embedded in the SOFA software.
123**
124** e) These requirements must be reproduced intact in any source
125** distribution and shall apply to anyone to whom you have
126** granted a further right to modify the source code of your
127** derived work.
128**
129** Note that, as originally distributed, the SOFA software is
130** intended to be a definitive implementation of the IAU standards,
131** and consequently third-party modifications are discouraged. All
132** variations, no matter how minor, must be explicitly marked as
133** such, as explained above.
134**
135** 4. You shall not cause the SOFA software to be brought into
136** disrepute, either by misuse, or use for inappropriate tasks, or
137** by inappropriate modification.
138**
139** 5. The SOFA software is provided "as is" and SOFA makes no warranty
140** as to its use or performance. SOFA does not and cannot warrant
141** the performance or results which the user may obtain by using the
142** SOFA software. SOFA makes no warranties, express or implied, as
143** to non-infringement of third party rights, merchantability, or
144** fitness for any particular purpose. In no event will SOFA be
145** liable to the user for any consequential, incidental, or special
146** damages, including any lost profits or lost savings, even if a
147** SOFA representative has been advised of such damages, or for any
148** claim by any third party.
149**
150** 6. The provision of any version of the SOFA software under the terms
151** and conditions specified herein does not imply that future
152** versions will also be made available under the same terms and
153** conditions.
154*
155** In any published work or commercial product which uses the SOFA
156** software directly, acknowledgement (see www.iausofa.org) is
157** appreciated.
158**
159** Correspondence concerning SOFA software should be addressed as
160** follows:
161**
162** By email: sofa@ukho.gov.uk
163** By post: IAU SOFA Center
164** HM Nautical Almanac Office
165** UK Hydrographic Office
166** Admiralty Way, Taunton
167** Somerset, TA1 2DN
168** United Kingdom
169**
170**--------------------------------------------------------------------*/
171}
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