source: trunk/FACT++/sofa/src/pr00.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
3void iauPr00(double date1, double date2, double *dpsipr, double *depspr)
4/*
5** - - - - - - - -
6** i a u P r 0 0
7** - - - - - - - -
8**
9** Precession-rate part of the IAU 2000 precession-nutation models
10** (part of MHB2000).
11**
12** This function is part of the International Astronomical Union's
13** SOFA (Standards Of Fundamental Astronomy) software collection.
14**
15** Status: canonical model.
16**
17** Given:
18** date1,date2 double TT as a 2-part Julian Date (Note 1)
19**
20** Returned:
21** dpsipr,depspr double precession corrections (Notes 2,3)
22**
23** Notes:
24**
25** 1) The TT date date1+date2 is a Julian Date, apportioned in any
26** convenient way between the two arguments. For example,
27** JD(TT)=2450123.7 could be expressed in any of these ways,
28** among others:
29**
30** date1 date2
31**
32** 2450123.7 0.0 (JD method)
33** 2451545.0 -1421.3 (J2000 method)
34** 2400000.5 50123.2 (MJD method)
35** 2450123.5 0.2 (date & time method)
36**
37** The JD method is the most natural and convenient to use in
38** cases where the loss of several decimal digits of resolution
39** is acceptable. The J2000 method is best matched to the way
40** the argument is handled internally and will deliver the
41** optimum resolution. The MJD method and the date & time methods
42** are both good compromises between resolution and convenience.
43**
44** 2) The precession adjustments are expressed as "nutation
45** components", corrections in longitude and obliquity with respect
46** to the J2000.0 equinox and ecliptic.
47**
48** 3) Although the precession adjustments are stated to be with respect
49** to Lieske et al. (1977), the MHB2000 model does not specify which
50** set of Euler angles are to be used and how the adjustments are to
51** be applied. The most literal and straightforward procedure is to
52** adopt the 4-rotation epsilon_0, psi_A, omega_A, xi_A option, and
53** to add dpsipr to psi_A and depspr to both omega_A and eps_A.
54**
55** 4) This is an implementation of one aspect of the IAU 2000A nutation
56** model, formally adopted by the IAU General Assembly in 2000,
57** namely MHB2000 (Mathews et al. 2002).
58**
59** References:
60**
61** Lieske, J.H., Lederle, T., Fricke, W. & Morando, B., "Expressions
62** for the precession quantities based upon the IAU (1976) System of
63** Astronomical Constants", Astron.Astrophys., 58, 1-16 (1977)
64**
65** Mathews, P.M., Herring, T.A., Buffet, B.A., "Modeling of nutation
66** and precession New nutation series for nonrigid Earth and
67** insights into the Earth's interior", J.Geophys.Res., 107, B4,
68** 2002. The MHB2000 code itself was obtained on 9th September 2002
69** from ftp://maia.usno.navy.mil/conv2000/chapter5/IAU2000A.
70**
71** Wallace, P.T., "Software for Implementing the IAU 2000
72** Resolutions", in IERS Workshop 5.1 (2002).
73**
74** This revision: 2013 June 18
75**
76** SOFA release 2015-02-09
77**
78** Copyright (C) 2015 IAU SOFA Board. See notes at end.
79*/
80{
81 double t;
82
83/* Precession and obliquity corrections (radians per century) */
84 static const double PRECOR = -0.29965 * DAS2R,
85 OBLCOR = -0.02524 * DAS2R;
86
87/* Interval between fundamental epoch J2000.0 and given date (JC). */
88 t = ((date1 - DJ00) + date2) / DJC;
89
90/* Precession rate contributions with respect to IAU 1976/80. */
91 *dpsipr = PRECOR * t;
92 *depspr = OBLCOR * t;
93
94 return;
95
96/*----------------------------------------------------------------------
97**
98** Copyright (C) 2015
99** Standards Of Fundamental Astronomy Board
100** of the International Astronomical Union.
101**
102** =====================
103** SOFA Software License
104** =====================
105**
106** NOTICE TO USER:
107**
108** BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
109** CONDITIONS WHICH APPLY TO ITS USE.
110**
111** 1. The Software is owned by the IAU SOFA Board ("SOFA").
112**
113** 2. Permission is granted to anyone to use the SOFA software for any
114** purpose, including commercial applications, free of charge and
115** without payment of royalties, subject to the conditions and
116** restrictions listed below.
117**
118** 3. You (the user) may copy and distribute SOFA source code to others,
119** and use and adapt its code and algorithms in your own software,
120** on a world-wide, royalty-free basis. That portion of your
121** distribution that does not consist of intact and unchanged copies
122** of SOFA source code files is a "derived work" that must comply
123** with the following requirements:
124**
125** a) Your work shall be marked or carry a statement that it
126** (i) uses routines and computations derived by you from
127** software provided by SOFA under license to you; and
128** (ii) does not itself constitute software provided by and/or
129** endorsed by SOFA.
130**
131** b) The source code of your derived work must contain descriptions
132** of how the derived work is based upon, contains and/or differs
133** from the original SOFA software.
134**
135** c) The names of all routines in your derived work shall not
136** include the prefix "iau" or "sofa" or trivial modifications
137** thereof such as changes of case.
138**
139** d) The origin of the SOFA components of your derived work must
140** not be misrepresented; you must not claim that you wrote the
141** original software, nor file a patent application for SOFA
142** software or algorithms embedded in the SOFA software.
143**
144** e) These requirements must be reproduced intact in any source
145** distribution and shall apply to anyone to whom you have
146** granted a further right to modify the source code of your
147** derived work.
148**
149** Note that, as originally distributed, the SOFA software is
150** intended to be a definitive implementation of the IAU standards,
151** and consequently third-party modifications are discouraged. All
152** variations, no matter how minor, must be explicitly marked as
153** such, as explained above.
154**
155** 4. You shall not cause the SOFA software to be brought into
156** disrepute, either by misuse, or use for inappropriate tasks, or
157** by inappropriate modification.
158**
159** 5. The SOFA software is provided "as is" and SOFA makes no warranty
160** as to its use or performance. SOFA does not and cannot warrant
161** the performance or results which the user may obtain by using the
162** SOFA software. SOFA makes no warranties, express or implied, as
163** to non-infringement of third party rights, merchantability, or
164** fitness for any particular purpose. In no event will SOFA be
165** liable to the user for any consequential, incidental, or special
166** damages, including any lost profits or lost savings, even if a
167** SOFA representative has been advised of such damages, or for any
168** claim by any third party.
169**
170** 6. The provision of any version of the SOFA software under the terms
171** and conditions specified herein does not imply that future
172** versions will also be made available under the same terms and
173** conditions.
174*
175** In any published work or commercial product which uses the SOFA
176** software directly, acknowledgement (see www.iausofa.org) is
177** appreciated.
178**
179** Correspondence concerning SOFA software should be addressed as
180** follows:
181**
182** By email: sofa@ukho.gov.uk
183** By post: IAU SOFA Center
184** HM Nautical Almanac Office
185** UK Hydrographic Office
186** Admiralty Way, Taunton
187** Somerset, TA1 2DN
188** United Kingdom
189**
190**--------------------------------------------------------------------*/
191}
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