source: trunk/FACT++/sofa/src/s06a.c@ 18355

Last change on this file since 18355 was 18346, checked in by tbretz, 11 years ago
File size: 7.6 KB
Line 
1#include "sofa.h"
2
3double iauS06a(double date1, double date2)
4/*
5** - - - - - - - -
6** i a u S 0 6 a
7** - - - - - - - -
8**
9** The CIO locator s, positioning the Celestial Intermediate Origin on
10** the equator of the Celestial Intermediate Pole, using the IAU 2006
11** precession and IAU 2000A nutation models.
12**
13** This function is part of the International Astronomical Union's
14** SOFA (Standards Of Fundamental Astronomy) software collection.
15**
16** Status: support function.
17**
18** Given:
19** date1,date2 double TT as a 2-part Julian Date (Note 1)
20**
21** Returned (function value):
22** double the CIO locator s in radians (Note 2)
23**
24** Notes:
25**
26** 1) The TT date date1+date2 is a Julian Date, apportioned in any
27** convenient way between the two arguments. For example,
28** JD(TT)=2450123.7 could be expressed in any of these ways,
29** among others:
30**
31** date1 date2
32**
33** 2450123.7 0.0 (JD method)
34** 2451545.0 -1421.3 (J2000 method)
35** 2400000.5 50123.2 (MJD method)
36** 2450123.5 0.2 (date & time method)
37**
38** The JD method is the most natural and convenient to use in
39** cases where the loss of several decimal digits of resolution
40** is acceptable. The J2000 method is best matched to the way
41** the argument is handled internally and will deliver the
42** optimum resolution. The MJD method and the date & time methods
43** are both good compromises between resolution and convenience.
44**
45** 2) The CIO locator s is the difference between the right ascensions
46** of the same point in two systems. The two systems are the GCRS
47** and the CIP,CIO, and the point is the ascending node of the
48** CIP equator. The CIO locator s remains a small fraction of
49** 1 arcsecond throughout 1900-2100.
50**
51** 3) The series used to compute s is in fact for s+XY/2, where X and Y
52** are the x and y components of the CIP unit vector; this series is
53** more compact than a direct series for s would be. The present
54** function uses the full IAU 2000A nutation model when predicting
55** the CIP position.
56**
57** Called:
58** iauPnm06a classical NPB matrix, IAU 2006/2000A
59** iauBpn2xy extract CIP X,Y coordinates from NPB matrix
60** iauS06 the CIO locator s, given X,Y, IAU 2006
61**
62** References:
63**
64** Capitaine, N., Chapront, J., Lambert, S. and Wallace, P.,
65** "Expressions for the Celestial Intermediate Pole and Celestial
66** Ephemeris Origin consistent with the IAU 2000A precession-
67** nutation model", Astron.Astrophys. 400, 1145-1154 (2003)
68**
69** n.b. The celestial ephemeris origin (CEO) was renamed "celestial
70** intermediate origin" (CIO) by IAU 2006 Resolution 2.
71**
72** Capitaine, N. & Wallace, P.T., 2006, Astron.Astrophys. 450, 855
73**
74** McCarthy, D. D., Petit, G. (eds.), 2004, IERS Conventions (2003),
75** IERS Technical Note No. 32, BKG
76**
77** Wallace, P.T. & Capitaine, N., 2006, Astron.Astrophys. 459, 981
78**
79** This revision: 2013 June 18
80**
81** SOFA release 2015-02-09
82**
83** Copyright (C) 2015 IAU SOFA Board. See notes at end.
84*/
85{
86 double rnpb[3][3], x, y, s;
87
88/* Bias-precession-nutation-matrix, IAU 20006/2000A. */
89 iauPnm06a(date1, date2, rnpb);
90
91/* Extract the CIP coordinates. */
92 iauBpn2xy(rnpb, &x, &y);
93
94/* Compute the CIO locator s, given the CIP coordinates. */
95 s = iauS06(date1, date2, x, y);
96
97 return s;
98
99/*----------------------------------------------------------------------
100**
101** Copyright (C) 2015
102** Standards Of Fundamental Astronomy Board
103** of the International Astronomical Union.
104**
105** =====================
106** SOFA Software License
107** =====================
108**
109** NOTICE TO USER:
110**
111** BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
112** CONDITIONS WHICH APPLY TO ITS USE.
113**
114** 1. The Software is owned by the IAU SOFA Board ("SOFA").
115**
116** 2. Permission is granted to anyone to use the SOFA software for any
117** purpose, including commercial applications, free of charge and
118** without payment of royalties, subject to the conditions and
119** restrictions listed below.
120**
121** 3. You (the user) may copy and distribute SOFA source code to others,
122** and use and adapt its code and algorithms in your own software,
123** on a world-wide, royalty-free basis. That portion of your
124** distribution that does not consist of intact and unchanged copies
125** of SOFA source code files is a "derived work" that must comply
126** with the following requirements:
127**
128** a) Your work shall be marked or carry a statement that it
129** (i) uses routines and computations derived by you from
130** software provided by SOFA under license to you; and
131** (ii) does not itself constitute software provided by and/or
132** endorsed by SOFA.
133**
134** b) The source code of your derived work must contain descriptions
135** of how the derived work is based upon, contains and/or differs
136** from the original SOFA software.
137**
138** c) The names of all routines in your derived work shall not
139** include the prefix "iau" or "sofa" or trivial modifications
140** thereof such as changes of case.
141**
142** d) The origin of the SOFA components of your derived work must
143** not be misrepresented; you must not claim that you wrote the
144** original software, nor file a patent application for SOFA
145** software or algorithms embedded in the SOFA software.
146**
147** e) These requirements must be reproduced intact in any source
148** distribution and shall apply to anyone to whom you have
149** granted a further right to modify the source code of your
150** derived work.
151**
152** Note that, as originally distributed, the SOFA software is
153** intended to be a definitive implementation of the IAU standards,
154** and consequently third-party modifications are discouraged. All
155** variations, no matter how minor, must be explicitly marked as
156** such, as explained above.
157**
158** 4. You shall not cause the SOFA software to be brought into
159** disrepute, either by misuse, or use for inappropriate tasks, or
160** by inappropriate modification.
161**
162** 5. The SOFA software is provided "as is" and SOFA makes no warranty
163** as to its use or performance. SOFA does not and cannot warrant
164** the performance or results which the user may obtain by using the
165** SOFA software. SOFA makes no warranties, express or implied, as
166** to non-infringement of third party rights, merchantability, or
167** fitness for any particular purpose. In no event will SOFA be
168** liable to the user for any consequential, incidental, or special
169** damages, including any lost profits or lost savings, even if a
170** SOFA representative has been advised of such damages, or for any
171** claim by any third party.
172**
173** 6. The provision of any version of the SOFA software under the terms
174** and conditions specified herein does not imply that future
175** versions will also be made available under the same terms and
176** conditions.
177*
178** In any published work or commercial product which uses the SOFA
179** software directly, acknowledgement (see www.iausofa.org) is
180** appreciated.
181**
182** Correspondence concerning SOFA software should be addressed as
183** follows:
184**
185** By email: sofa@ukho.gov.uk
186** By post: IAU SOFA Center
187** HM Nautical Almanac Office
188** UK Hydrographic Office
189** Admiralty Way, Taunton
190** Somerset, TA1 2DN
191** United Kingdom
192**
193**--------------------------------------------------------------------*/
194}
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