source: trunk/FACT++/erfa/src/eo06a.c

Last change on this file was 18921, checked in by tbretz, 7 years ago
Updated to ERFA 1.4.0
File size: 5.4 KB
Line 
1#include "erfa.h"
2
3double eraEo06a(double date1, double date2)
4/*
5** - - - - - - - - -
6** e r a E o 0 6 a
7** - - - - - - - - -
8**
9** Equation of the origins, IAU 2006 precession and IAU 2000A nutation.
10**
11** Given:
12** date1,date2 double TT as a 2-part Julian Date (Note 1)
13**
14** Returned (function value):
15** double equation of the origins in radians
16**
17** Notes:
18**
19** 1) The TT date date1+date2 is a Julian Date, apportioned in any
20** convenient way between the two arguments. For example,
21** JD(TT)=2450123.7 could be expressed in any of these ways,
22** among others:
23**
24** date1 date2
25**
26** 2450123.7 0.0 (JD method)
27** 2451545.0 -1421.3 (J2000 method)
28** 2400000.5 50123.2 (MJD method)
29** 2450123.5 0.2 (date & time method)
30**
31** The JD method is the most natural and convenient to use in
32** cases where the loss of several decimal digits of resolution
33** is acceptable. The J2000 method is best matched to the way
34** the argument is handled internally and will deliver the
35** optimum resolution. The MJD method and the date & time methods
36** are both good compromises between resolution and convenience.
37**
38** 2) The equation of the origins is the distance between the true
39** equinox and the celestial intermediate origin and, equivalently,
40** the difference between Earth rotation angle and Greenwich
41** apparent sidereal time (ERA-GST). It comprises the precession
42** (since J2000.0) in right ascension plus the equation of the
43** equinoxes (including the small correction terms).
44**
45** Called:
46** eraPnm06a classical NPB matrix, IAU 2006/2000A
47** eraBpn2xy extract CIP X,Y coordinates from NPB matrix
48** eraS06 the CIO locator s, given X,Y, IAU 2006
49** eraEors equation of the origins, given NPB matrix and s
50**
51** References:
52**
53** Capitaine, N. & Wallace, P.T., 2006, Astron.Astrophys. 450, 855
54**
55** Wallace, P.T. & Capitaine, N., 2006, Astron.Astrophys. 459, 981
56**
57** Copyright (C) 2013-2017, NumFOCUS Foundation.
58** Derived, with permission, from the SOFA library. See notes at end of file.
59*/
60{
61 double r[3][3], x, y, s, eo;
62
63
64/* Classical nutation x precession x bias matrix. */
65 eraPnm06a(date1, date2, r);
66
67/* Extract CIP coordinates. */
68 eraBpn2xy(r, &x, &y);
69
70/* The CIO locator, s. */
71 s = eraS06(date1, date2, x, y);
72
73/* Solve for the EO. */
74 eo = eraEors(r, s);
75
76 return eo;
77
78}
79/*----------------------------------------------------------------------
80**
81**
82** Copyright (C) 2013-2017, NumFOCUS Foundation.
83** All rights reserved.
84**
85** This library is derived, with permission, from the International
86** Astronomical Union's "Standards of Fundamental Astronomy" library,
87** available from http://www.iausofa.org.
88**
89** The ERFA version is intended to retain identical functionality to
90** the SOFA library, but made distinct through different function and
91** file names, as set out in the SOFA license conditions. The SOFA
92** original has a role as a reference standard for the IAU and IERS,
93** and consequently redistribution is permitted only in its unaltered
94** state. The ERFA version is not subject to this restriction and
95** therefore can be included in distributions which do not support the
96** concept of "read only" software.
97**
98** Although the intent is to replicate the SOFA API (other than
99** replacement of prefix names) and results (with the exception of
100** bugs; any that are discovered will be fixed), SOFA is not
101** responsible for any errors found in this version of the library.
102**
103** If you wish to acknowledge the SOFA heritage, please acknowledge
104** that you are using a library derived from SOFA, rather than SOFA
105** itself.
106**
107**
108** TERMS AND CONDITIONS
109**
110** Redistribution and use in source and binary forms, with or without
111** modification, are permitted provided that the following conditions
112** are met:
113**
114** 1 Redistributions of source code must retain the above copyright
115** notice, this list of conditions and the following disclaimer.
116**
117** 2 Redistributions in binary form must reproduce the above copyright
118** notice, this list of conditions and the following disclaimer in
119** the documentation and/or other materials provided with the
120** distribution.
121**
122** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
123** the International Astronomical Union nor the names of its
124** contributors may be used to endorse or promote products derived
125** from this software without specific prior written permission.
126**
127** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
128** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
129** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
130** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
131** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
132** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
133** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
134** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
135** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
136** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
137** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
138** POSSIBILITY OF SUCH DAMAGE.
139**
140*/
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