source: trunk/FACT++/erfa/src/xys00b.c@ 18350

Last change on this file since 18350 was 18348, checked in by tbretz, 9 years ago
File size: 5.4 KB
Line 
1#include "erfa.h"
2
3void eraXys00b(double date1, double date2,
4 double *x, double *y, double *s)
5/*
6** - - - - - - - - - -
7** e r a X y s 0 0 b
8** - - - - - - - - - -
9**
10** For a given TT date, compute the X,Y coordinates of the Celestial
11** Intermediate Pole and the CIO locator s, using the IAU 2000B
12** precession-nutation model.
13**
14** Given:
15** date1,date2 double TT as a 2-part Julian Date (Note 1)
16**
17** Returned:
18** x,y double Celestial Intermediate Pole (Note 2)
19** s double the CIO locator s (Note 2)
20**
21** Notes:
22**
23** 1) The TT date date1+date2 is a Julian Date, apportioned in any
24** convenient way between the two arguments. For example,
25** JD(TT)=2450123.7 could be expressed in any of these ways,
26** among others:
27**
28** date1 date2
29**
30** 2450123.7 0.0 (JD method)
31** 2451545.0 -1421.3 (J2000 method)
32** 2400000.5 50123.2 (MJD method)
33** 2450123.5 0.2 (date & time method)
34**
35** The JD method is the most natural and convenient to use in
36** cases where the loss of several decimal digits of resolution
37** is acceptable. The J2000 method is best matched to the way
38** the argument is handled internally and will deliver the
39** optimum resolution. The MJD method and the date & time methods
40** are both good compromises between resolution and convenience.
41**
42** 2) The Celestial Intermediate Pole coordinates are the x,y
43** components of the unit vector in the Geocentric Celestial
44** Reference System.
45**
46** 3) The CIO locator s (in radians) positions the Celestial
47** Intermediate Origin on the equator of the CIP.
48**
49** 4) The present function is faster, but slightly less accurate (about
50** 1 mas in X,Y), than the eraXys00a function.
51**
52** Called:
53** eraPnm00b classical NPB matrix, IAU 2000B
54** eraBpn2xy extract CIP X,Y coordinates from NPB matrix
55** eraS00 the CIO locator s, given X,Y, IAU 2000A
56**
57** Reference:
58**
59** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
60** IERS Technical Note No. 32, BKG (2004)
61**
62** Copyright (C) 2013-2015, NumFOCUS Foundation.
63** Derived, with permission, from the SOFA library. See notes at end of file.
64*/
65{
66 double rbpn[3][3];
67
68/* Form the bias-precession-nutation matrix, IAU 2000A. */
69 eraPnm00b(date1, date2, rbpn);
70
71/* Extract X,Y. */
72 eraBpn2xy(rbpn, x, y);
73
74/* Obtain s. */
75 *s = eraS00(date1, date2, *x, *y);
76
77 return;
78
79}
80/*----------------------------------------------------------------------
81**
82**
83** Copyright (C) 2013-2015, NumFOCUS Foundation.
84** All rights reserved.
85**
86** This library is derived, with permission, from the International
87** Astronomical Union's "Standards of Fundamental Astronomy" library,
88** available from http://www.iausofa.org.
89**
90** The ERFA version is intended to retain identical functionality to
91** the SOFA library, but made distinct through different function and
92** file names, as set out in the SOFA license conditions. The SOFA
93** original has a role as a reference standard for the IAU and IERS,
94** and consequently redistribution is permitted only in its unaltered
95** state. The ERFA version is not subject to this restriction and
96** therefore can be included in distributions which do not support the
97** concept of "read only" software.
98**
99** Although the intent is to replicate the SOFA API (other than
100** replacement of prefix names) and results (with the exception of
101** bugs; any that are discovered will be fixed), SOFA is not
102** responsible for any errors found in this version of the library.
103**
104** If you wish to acknowledge the SOFA heritage, please acknowledge
105** that you are using a library derived from SOFA, rather than SOFA
106** itself.
107**
108**
109** TERMS AND CONDITIONS
110**
111** Redistribution and use in source and binary forms, with or without
112** modification, are permitted provided that the following conditions
113** are met:
114**
115** 1 Redistributions of source code must retain the above copyright
116** notice, this list of conditions and the following disclaimer.
117**
118** 2 Redistributions in binary form must reproduce the above copyright
119** notice, this list of conditions and the following disclaimer in
120** the documentation and/or other materials provided with the
121** distribution.
122**
123** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
124** the International Astronomical Union nor the names of its
125** contributors may be used to endorse or promote products derived
126** from this software without specific prior written permission.
127**
128** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
129** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
130** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
131** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
132** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
133** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
134** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
135** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
136** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
137** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
138** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
139** POSSIBILITY OF SUCH DAMAGE.
140**
141*/
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