source: trunk/FACT++/erfa/src/s00b.c@ 18403

Last change on this file since 18403 was 18348, checked in by tbretz, 9 years ago
File size: 6.2 KB
Line 
1#include "erfa.h"
2
3double eraS00b(double date1, double date2)
4/*
5** - - - - - - - -
6** e r a S 0 0 b
7** - - - - - - - -
8**
9** The CIO locator s, positioning the Celestial Intermediate Origin on
10** the equator of the Celestial Intermediate Pole, using the IAU 2000B
11** precession-nutation model.
12**
13** Given:
14** date1,date2 double TT as a 2-part Julian Date (Note 1)
15**
16** Returned (function value):
17** double the CIO locator s in radians (Note 2)
18**
19** Notes:
20**
21** 1) The TT date date1+date2 is a Julian Date, apportioned in any
22** convenient way between the two arguments. For example,
23** JD(TT)=2450123.7 could be expressed in any of these ways,
24** among others:
25**
26** date1 date2
27**
28** 2450123.7 0.0 (JD method)
29** 2451545.0 -1421.3 (J2000 method)
30** 2400000.5 50123.2 (MJD method)
31** 2450123.5 0.2 (date & time method)
32**
33** The JD method is the most natural and convenient to use in
34** cases where the loss of several decimal digits of resolution
35** is acceptable. The J2000 method is best matched to the way
36** the argument is handled internally and will deliver the
37** optimum resolution. The MJD method and the date & time methods
38** are both good compromises between resolution and convenience.
39**
40** 2) The CIO locator s is the difference between the right ascensions
41** of the same point in two systems. The two systems are the GCRS
42** and the CIP,CIO, and the point is the ascending node of the
43** CIP equator. The CIO locator s remains a small fraction of
44** 1 arcsecond throughout 1900-2100.
45**
46** 3) The series used to compute s is in fact for s+XY/2, where X and Y
47** are the x and y components of the CIP unit vector; this series
48** is more compact than a direct series for s would be. The present
49** function uses the IAU 2000B truncated nutation model when
50** predicting the CIP position. The function eraS00a uses instead
51** the full IAU 2000A model, but with no significant increase in
52** accuracy and at some cost in speed.
53**
54** Called:
55** eraPnm00b classical NPB matrix, IAU 2000B
56** eraBnp2xy extract CIP X,Y from the BPN matrix
57** eraS00 the CIO locator s, given X,Y, IAU 2000A
58**
59** References:
60**
61** Capitaine, N., Chapront, J., Lambert, S. and Wallace, P.,
62** "Expressions for the Celestial Intermediate Pole and Celestial
63** Ephemeris Origin consistent with the IAU 2000A precession-
64** nutation model", Astron.Astrophys. 400, 1145-1154 (2003)
65**
66** n.b. The celestial ephemeris origin (CEO) was renamed "celestial
67** intermediate origin" (CIO) by IAU 2006 Resolution 2.
68**
69** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
70** IERS Technical Note No. 32, BKG (2004)
71**
72** Copyright (C) 2013-2015, NumFOCUS Foundation.
73** Derived, with permission, from the SOFA library. See notes at end of file.
74*/
75{
76 double rbpn[3][3], x, y, s;
77
78/* Bias-precession-nutation-matrix, IAU 2000B. */
79 eraPnm00b(date1, date2, rbpn);
80
81/* Extract the CIP coordinates. */
82 eraBpn2xy(rbpn, &x, &y);
83
84/* Compute the CIO locator s, given the CIP coordinates. */
85 s = eraS00(date1, date2, x, y);
86
87 return s;
88
89}
90/*----------------------------------------------------------------------
91**
92**
93** Copyright (C) 2013-2015, NumFOCUS Foundation.
94** All rights reserved.
95**
96** This library is derived, with permission, from the International
97** Astronomical Union's "Standards of Fundamental Astronomy" library,
98** available from http://www.iausofa.org.
99**
100** The ERFA version is intended to retain identical functionality to
101** the SOFA library, but made distinct through different function and
102** file names, as set out in the SOFA license conditions. The SOFA
103** original has a role as a reference standard for the IAU and IERS,
104** and consequently redistribution is permitted only in its unaltered
105** state. The ERFA version is not subject to this restriction and
106** therefore can be included in distributions which do not support the
107** concept of "read only" software.
108**
109** Although the intent is to replicate the SOFA API (other than
110** replacement of prefix names) and results (with the exception of
111** bugs; any that are discovered will be fixed), SOFA is not
112** responsible for any errors found in this version of the library.
113**
114** If you wish to acknowledge the SOFA heritage, please acknowledge
115** that you are using a library derived from SOFA, rather than SOFA
116** itself.
117**
118**
119** TERMS AND CONDITIONS
120**
121** Redistribution and use in source and binary forms, with or without
122** modification, are permitted provided that the following conditions
123** are met:
124**
125** 1 Redistributions of source code must retain the above copyright
126** notice, this list of conditions and the following disclaimer.
127**
128** 2 Redistributions in binary form must reproduce the above copyright
129** notice, this list of conditions and the following disclaimer in
130** the documentation and/or other materials provided with the
131** distribution.
132**
133** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
134** the International Astronomical Union nor the names of its
135** contributors may be used to endorse or promote products derived
136** from this software without specific prior written permission.
137**
138** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
139** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
140** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
141** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
142** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
143** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
144** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
145** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
146** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
147** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
148** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
149** POSSIBILITY OF SUCH DAMAGE.
150**
151*/
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