source: branches/FACT++_part_filenames/erfa/src/eors.c@ 18732

Last change on this file since 18732 was 18711, checked in by tbretz, 8 years ago
Updated to ERFA 1.3.0 (no relevant code change except the leap second at the beginning of 2017)
File size: 4.5 KB
Line 
1#include "erfa.h"
2
3double eraEors(double rnpb[3][3], double s)
4/*
5** - - - - - - - -
6** e r a E o r s
7** - - - - - - - -
8**
9** Equation of the origins, given the classical NPB matrix and the
10** quantity s.
11**
12** Given:
13** rnpb double[3][3] classical nutation x precession x bias matrix
14** s double the quantity s (the CIO locator)
15**
16** Returned (function value):
17** double the equation of the origins in radians.
18**
19** Notes:
20**
21** 1) The equation of the origins is the distance between the true
22** equinox and the celestial intermediate origin and, equivalently,
23** the difference between Earth rotation angle and Greenwich
24** apparent sidereal time (ERA-GST). It comprises the precession
25** (since J2000.0) in right ascension plus the equation of the
26** equinoxes (including the small correction terms).
27**
28** 2) The algorithm is from Wallace & Capitaine (2006).
29**
30** References:
31**
32** Capitaine, N. & Wallace, P.T., 2006, Astron.Astrophys. 450, 855
33**
34** Wallace, P. & Capitaine, N., 2006, Astron.Astrophys. 459, 981
35**
36** Copyright (C) 2013-2016, NumFOCUS Foundation.
37** Derived, with permission, from the SOFA library. See notes at end of file.
38*/
39{
40 double x, ax, xs, ys, zs, p, q, eo;
41
42
43/* Evaluate Wallace & Capitaine (2006) expression (16). */
44 x = rnpb[2][0];
45 ax = x / (1.0 + rnpb[2][2]);
46 xs = 1.0 - ax * x;
47 ys = -ax * rnpb[2][1];
48 zs = -x;
49 p = rnpb[0][0] * xs + rnpb[0][1] * ys + rnpb[0][2] * zs;
50 q = rnpb[1][0] * xs + rnpb[1][1] * ys + rnpb[1][2] * zs;
51 eo = ((p != 0) || (q != 0)) ? s - atan2(q, p) : s;
52
53 return eo;
54
55}
56/*----------------------------------------------------------------------
57**
58**
59** Copyright (C) 2013-2016, NumFOCUS Foundation.
60** All rights reserved.
61**
62** This library is derived, with permission, from the International
63** Astronomical Union's "Standards of Fundamental Astronomy" library,
64** available from http://www.iausofa.org.
65**
66** The ERFA version is intended to retain identical functionality to
67** the SOFA library, but made distinct through different function and
68** file names, as set out in the SOFA license conditions. The SOFA
69** original has a role as a reference standard for the IAU and IERS,
70** and consequently redistribution is permitted only in its unaltered
71** state. The ERFA version is not subject to this restriction and
72** therefore can be included in distributions which do not support the
73** concept of "read only" software.
74**
75** Although the intent is to replicate the SOFA API (other than
76** replacement of prefix names) and results (with the exception of
77** bugs; any that are discovered will be fixed), SOFA is not
78** responsible for any errors found in this version of the library.
79**
80** If you wish to acknowledge the SOFA heritage, please acknowledge
81** that you are using a library derived from SOFA, rather than SOFA
82** itself.
83**
84**
85** TERMS AND CONDITIONS
86**
87** Redistribution and use in source and binary forms, with or without
88** modification, are permitted provided that the following conditions
89** are met:
90**
91** 1 Redistributions of source code must retain the above copyright
92** notice, this list of conditions and the following disclaimer.
93**
94** 2 Redistributions in binary form must reproduce the above copyright
95** notice, this list of conditions and the following disclaimer in
96** the documentation and/or other materials provided with the
97** distribution.
98**
99** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
100** the International Astronomical Union nor the names of its
101** contributors may be used to endorse or promote products derived
102** from this software without specific prior written permission.
103**
104** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
105** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
106** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
107** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
108** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
109** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
110** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
111** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
112** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
113** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
114** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
115** POSSIBILITY OF SUCH DAMAGE.
116**
117*/
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