source: trunk/FACT++/sofa/src/atic13.c@ 18368

Last change on this file since 18368 was 18346, checked in by tbretz, 11 years ago
File size: 7.7 KB
Line 
1#include "sofa.h"
2
3void iauAtic13(double ri, double di, double date1, double date2,
4 double *rc, double *dc, double *eo)
5/*
6** - - - - - - - - - -
7** i a u A t i c 1 3
8** - - - - - - - - - -
9**
10** Transform star RA,Dec from geocentric CIRS to ICRS astrometric.
11**
12** This function is part of the International Astronomical Union's
13** SOFA (Standards of Fundamental Astronomy) software collection.
14**
15** Status: support function.
16**
17** Given:
18** ri,di double CIRS geocentric RA,Dec (radians)
19** date1 double TDB as a 2-part...
20** date2 double ...Julian Date (Note 1)
21**
22** Returned:
23** rc,dc double ICRS astrometric RA,Dec (radians)
24** eo double equation of the origins (ERA-GST, Note 4)
25**
26** Notes:
27**
28** 1) The TDB date date1+date2 is a Julian Date, apportioned in any
29** convenient way between the two arguments. For example,
30** JD(TDB)=2450123.7 could be expressed in any of these ways, among
31** others:
32**
33** date1 date2
34**
35** 2450123.7 0.0 (JD method)
36** 2451545.0 -1421.3 (J2000 method)
37** 2400000.5 50123.2 (MJD method)
38** 2450123.5 0.2 (date & time method)
39**
40** The JD method is the most natural and convenient to use in cases
41** where the loss of several decimal digits of resolution is
42** acceptable. The J2000 method is best matched to the way the
43** argument is handled internally and will deliver the optimum
44** resolution. The MJD method and the date & time methods are both
45** good compromises between resolution and convenience. For most
46** applications of this function the choice will not be at all
47** critical.
48**
49** TT can be used instead of TDB without any significant impact on
50** accuracy.
51**
52** 2) Iterative techniques are used for the aberration and light
53** deflection corrections so that the functions iauAtic13 (or
54** iauAticq) and iauAtci13 (or iauAtciq) are accurate inverses;
55** even at the edge of the Sun's disk the discrepancy is only about
56** 1 nanoarcsecond.
57**
58** 3) The available accuracy is better than 1 milliarcsecond, limited
59** mainly by the precession-nutation model that is used, namely
60** IAU 2000A/2006. Very close to solar system bodies, additional
61** errors of up to several milliarcseconds can occur because of
62** unmodeled light deflection; however, the Sun's contribution is
63** taken into account, to first order. The accuracy limitations of
64** the SOFA function iauEpv00 (used to compute Earth position and
65** velocity) can contribute aberration errors of up to
66** 5 microarcseconds. Light deflection at the Sun's limb is
67** uncertain at the 0.4 mas level.
68**
69** 4) Should the transformation to (equinox based) J2000.0 mean place
70** be required rather than (CIO based) ICRS coordinates, subtract the
71** equation of the origins from the returned right ascension:
72** RA = RI - EO. (The iauAnp function can then be applied, as
73** required, to keep the result in the conventional 0-2pi range.)
74**
75** Called:
76** iauApci13 astrometry parameters, ICRS-CIRS, 2013
77** iauAticq quick CIRS to ICRS astrometric
78**
79** This revision: 2013 October 9
80**
81** SOFA release 2015-02-09
82**
83** Copyright (C) 2015 IAU SOFA Board. See notes at end.
84*/
85{
86/* Star-independent astrometry parameters */
87 iauASTROM astrom;
88
89/* Star-independent astrometry parameters. */
90 iauApci13(date1, date2, &astrom, eo);
91
92/* CIRS to ICRS astrometric. */
93 iauAticq(ri, di, &astrom, rc, dc);
94
95/* Finished. */
96
97/*----------------------------------------------------------------------
98**
99** Copyright (C) 2015
100** Standards Of Fundamental Astronomy Board
101** of the International Astronomical Union.
102**
103** =====================
104** SOFA Software License
105** =====================
106**
107** NOTICE TO USER:
108**
109** BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
110** CONDITIONS WHICH APPLY TO ITS USE.
111**
112** 1. The Software is owned by the IAU SOFA Board ("SOFA").
113**
114** 2. Permission is granted to anyone to use the SOFA software for any
115** purpose, including commercial applications, free of charge and
116** without payment of royalties, subject to the conditions and
117** restrictions listed below.
118**
119** 3. You (the user) may copy and distribute SOFA source code to others,
120** and use and adapt its code and algorithms in your own software,
121** on a world-wide, royalty-free basis. That portion of your
122** distribution that does not consist of intact and unchanged copies
123** of SOFA source code files is a "derived work" that must comply
124** with the following requirements:
125**
126** a) Your work shall be marked or carry a statement that it
127** (i) uses routines and computations derived by you from
128** software provided by SOFA under license to you; and
129** (ii) does not itself constitute software provided by and/or
130** endorsed by SOFA.
131**
132** b) The source code of your derived work must contain descriptions
133** of how the derived work is based upon, contains and/or differs
134** from the original SOFA software.
135**
136** c) The names of all routines in your derived work shall not
137** include the prefix "iau" or "sofa" or trivial modifications
138** thereof such as changes of case.
139**
140** d) The origin of the SOFA components of your derived work must
141** not be misrepresented; you must not claim that you wrote the
142** original software, nor file a patent application for SOFA
143** software or algorithms embedded in the SOFA software.
144**
145** e) These requirements must be reproduced intact in any source
146** distribution and shall apply to anyone to whom you have
147** granted a further right to modify the source code of your
148** derived work.
149**
150** Note that, as originally distributed, the SOFA software is
151** intended to be a definitive implementation of the IAU standards,
152** and consequently third-party modifications are discouraged. All
153** variations, no matter how minor, must be explicitly marked as
154** such, as explained above.
155**
156** 4. You shall not cause the SOFA software to be brought into
157** disrepute, either by misuse, or use for inappropriate tasks, or
158** by inappropriate modification.
159**
160** 5. The SOFA software is provided "as is" and SOFA makes no warranty
161** as to its use or performance. SOFA does not and cannot warrant
162** the performance or results which the user may obtain by using the
163** SOFA software. SOFA makes no warranties, express or implied, as
164** to non-infringement of third party rights, merchantability, or
165** fitness for any particular purpose. In no event will SOFA be
166** liable to the user for any consequential, incidental, or special
167** damages, including any lost profits or lost savings, even if a
168** SOFA representative has been advised of such damages, or for any
169** claim by any third party.
170**
171** 6. The provision of any version of the SOFA software under the terms
172** and conditions specified herein does not imply that future
173** versions will also be made available under the same terms and
174** conditions.
175*
176** In any published work or commercial product which uses the SOFA
177** software directly, acknowledgement (see www.iausofa.org) is
178** appreciated.
179**
180** Correspondence concerning SOFA software should be addressed as
181** follows:
182**
183** By email: sofa@ukho.gov.uk
184** By post: IAU SOFA Center
185** HM Nautical Almanac Office
186** UK Hydrographic Office
187** Admiralty Way, Taunton
188** Somerset, TA1 2DN
189** United Kingdom
190**
191**--------------------------------------------------------------------*/
192
193}
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