source: trunk/FACT++/sofa/src/era00.c@ 18365

Last change on this file since 18365 was 18346, checked in by tbretz, 10 years ago
File size: 6.8 KB
Line 
1#include "sofa.h"
2
3double iauEra00(double dj1, double dj2)
4/*
5** - - - - - - - - -
6** i a u E r a 0 0
7** - - - - - - - - -
8**
9** Earth rotation angle (IAU 2000 model).
10**
11** This function is part of the International Astronomical Union's
12** SOFA (Standards Of Fundamental Astronomy) software collection.
13**
14** Status: canonical model.
15**
16** Given:
17** dj1,dj2 double UT1 as a 2-part Julian Date (see note)
18**
19** Returned (function value):
20** double Earth rotation angle (radians), range 0-2pi
21**
22** Notes:
23**
24** 1) The UT1 date dj1+dj2 is a Julian Date, apportioned in any
25** convenient way between the arguments dj1 and dj2. For example,
26** JD(UT1)=2450123.7 could be expressed in any of these ways,
27** among others:
28**
29** dj1 dj2
30**
31** 2450123.7 0.0 (JD method)
32** 2451545.0 -1421.3 (J2000 method)
33** 2400000.5 50123.2 (MJD method)
34** 2450123.5 0.2 (date & time method)
35**
36** The JD method is the most natural and convenient to use in
37** cases where the loss of several decimal digits of resolution
38** is acceptable. The J2000 and MJD methods are good compromises
39** between resolution and convenience. The date & time method is
40** best matched to the algorithm used: maximum precision is
41** delivered when the dj1 argument is for 0hrs UT1 on the day in
42** question and the dj2 argument lies in the range 0 to 1, or vice
43** versa.
44**
45** 2) The algorithm is adapted from Expression 22 of Capitaine et al.
46** 2000. The time argument has been expressed in days directly,
47** and, to retain precision, integer contributions have been
48** eliminated. The same formulation is given in IERS Conventions
49** (2003), Chap. 5, Eq. 14.
50**
51** Called:
52** iauAnp normalize angle into range 0 to 2pi
53**
54** References:
55**
56** Capitaine N., Guinot B. and McCarthy D.D, 2000, Astron.
57** Astrophys., 355, 398-405.
58**
59** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
60** IERS Technical Note No. 32, BKG (2004)
61**
62** This revision: 2013 June 18
63**
64** SOFA release 2015-02-09
65**
66** Copyright (C) 2015 IAU SOFA Board. See notes at end.
67*/
68{
69 double d1, d2, t, f, theta;
70
71/* Days since fundamental epoch. */
72 if (dj1 < dj2) {
73 d1 = dj1;
74 d2 = dj2;
75 } else {
76 d1 = dj2;
77 d2 = dj1;
78 }
79 t = d1 + (d2- DJ00);
80
81/* Fractional part of T (days). */
82 f = fmod(d1, 1.0) + fmod(d2, 1.0);
83
84/* Earth rotation angle at this UT1. */
85 theta = iauAnp(D2PI * (f + 0.7790572732640
86 + 0.00273781191135448 * t));
87
88 return theta;
89
90/*----------------------------------------------------------------------
91**
92** Copyright (C) 2015
93** Standards Of Fundamental Astronomy Board
94** of the International Astronomical Union.
95**
96** =====================
97** SOFA Software License
98** =====================
99**
100** NOTICE TO USER:
101**
102** BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
103** CONDITIONS WHICH APPLY TO ITS USE.
104**
105** 1. The Software is owned by the IAU SOFA Board ("SOFA").
106**
107** 2. Permission is granted to anyone to use the SOFA software for any
108** purpose, including commercial applications, free of charge and
109** without payment of royalties, subject to the conditions and
110** restrictions listed below.
111**
112** 3. You (the user) may copy and distribute SOFA source code to others,
113** and use and adapt its code and algorithms in your own software,
114** on a world-wide, royalty-free basis. That portion of your
115** distribution that does not consist of intact and unchanged copies
116** of SOFA source code files is a "derived work" that must comply
117** with the following requirements:
118**
119** a) Your work shall be marked or carry a statement that it
120** (i) uses routines and computations derived by you from
121** software provided by SOFA under license to you; and
122** (ii) does not itself constitute software provided by and/or
123** endorsed by SOFA.
124**
125** b) The source code of your derived work must contain descriptions
126** of how the derived work is based upon, contains and/or differs
127** from the original SOFA software.
128**
129** c) The names of all routines in your derived work shall not
130** include the prefix "iau" or "sofa" or trivial modifications
131** thereof such as changes of case.
132**
133** d) The origin of the SOFA components of your derived work must
134** not be misrepresented; you must not claim that you wrote the
135** original software, nor file a patent application for SOFA
136** software or algorithms embedded in the SOFA software.
137**
138** e) These requirements must be reproduced intact in any source
139** distribution and shall apply to anyone to whom you have
140** granted a further right to modify the source code of your
141** derived work.
142**
143** Note that, as originally distributed, the SOFA software is
144** intended to be a definitive implementation of the IAU standards,
145** and consequently third-party modifications are discouraged. All
146** variations, no matter how minor, must be explicitly marked as
147** such, as explained above.
148**
149** 4. You shall not cause the SOFA software to be brought into
150** disrepute, either by misuse, or use for inappropriate tasks, or
151** by inappropriate modification.
152**
153** 5. The SOFA software is provided "as is" and SOFA makes no warranty
154** as to its use or performance. SOFA does not and cannot warrant
155** the performance or results which the user may obtain by using the
156** SOFA software. SOFA makes no warranties, express or implied, as
157** to non-infringement of third party rights, merchantability, or
158** fitness for any particular purpose. In no event will SOFA be
159** liable to the user for any consequential, incidental, or special
160** damages, including any lost profits or lost savings, even if a
161** SOFA representative has been advised of such damages, or for any
162** claim by any third party.
163**
164** 6. The provision of any version of the SOFA software under the terms
165** and conditions specified herein does not imply that future
166** versions will also be made available under the same terms and
167** conditions.
168*
169** In any published work or commercial product which uses the SOFA
170** software directly, acknowledgement (see www.iausofa.org) is
171** appreciated.
172**
173** Correspondence concerning SOFA software should be addressed as
174** follows:
175**
176** By email: sofa@ukho.gov.uk
177** By post: IAU SOFA Center
178** HM Nautical Almanac Office
179** UK Hydrographic Office
180** Admiralty Way, Taunton
181** Somerset, TA1 2DN
182** United Kingdom
183**
184**--------------------------------------------------------------------*/
185}
Note: See TracBrowser for help on using the repository browser.