source: trunk/FACT++/erfa/src/gst06a.c@ 18403

Last change on this file since 18403 was 18348, checked in by tbretz, 9 years ago
File size: 5.6 KB
Line 
1#include "erfa.h"
2
3double eraGst06a(double uta, double utb, double tta, double ttb)
4/*
5** - - - - - - - - - -
6** e r a G s t 0 6 a
7** - - - - - - - - - -
8**
9** Greenwich apparent sidereal time (consistent with IAU 2000 and 2006
10** resolutions).
11**
12** Given:
13** uta,utb double UT1 as a 2-part Julian Date (Notes 1,2)
14** tta,ttb double TT as a 2-part Julian Date (Notes 1,2)
15**
16** Returned (function value):
17** double Greenwich apparent sidereal time (radians)
18**
19** Notes:
20**
21** 1) The UT1 and TT dates uta+utb and tta+ttb respectively, are both
22** Julian Dates, apportioned in any convenient way between the
23** argument pairs. For example, JD=2450123.7 could be expressed in
24** any of these ways, among others:
25**
26** Part A Part B
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 (in the case of UT; the TT is not at all critical
36** in this respect). The J2000 and MJD methods are good compromises
37** between resolution and convenience. For UT, the date & time
38** method is best matched to the algorithm that is used by the Earth
39** rotation angle function, called internally: maximum precision is
40** delivered when the uta argument is for 0hrs UT1 on the day in
41** question and the utb argument lies in the range 0 to 1, or vice
42** versa.
43**
44** 2) Both UT1 and TT are required, UT1 to predict the Earth rotation
45** and TT to predict the effects of precession-nutation. If UT1 is
46** used for both purposes, errors of order 100 microarcseconds
47** result.
48**
49** 3) This GAST is compatible with the IAU 2000/2006 resolutions and
50** must be used only in conjunction with IAU 2006 precession and
51** IAU 2000A nutation.
52**
53** 4) The result is returned in the range 0 to 2pi.
54**
55** Called:
56** eraPnm06a classical NPB matrix, IAU 2006/2000A
57** eraGst06 Greenwich apparent ST, IAU 2006, given NPB matrix
58**
59** Reference:
60**
61** Wallace, P.T. & Capitaine, N., 2006, Astron.Astrophys. 459, 981
62**
63** Copyright (C) 2013-2015, NumFOCUS Foundation.
64** Derived, with permission, from the SOFA library. See notes at end of file.
65*/
66{
67 double rnpb[3][3], gst;
68
69/* Classical nutation x precession x bias matrix, IAU 2000A. */
70 eraPnm06a(tta, ttb, rnpb);
71
72/* Greenwich apparent sidereal time. */
73 gst = eraGst06(uta, utb, tta, ttb, rnpb);
74
75 return gst;
76
77}
78/*----------------------------------------------------------------------
79**
80**
81** Copyright (C) 2013-2015, NumFOCUS Foundation.
82** All rights reserved.
83**
84** This library is derived, with permission, from the International
85** Astronomical Union's "Standards of Fundamental Astronomy" library,
86** available from http://www.iausofa.org.
87**
88** The ERFA version is intended to retain identical functionality to
89** the SOFA library, but made distinct through different function and
90** file names, as set out in the SOFA license conditions. The SOFA
91** original has a role as a reference standard for the IAU and IERS,
92** and consequently redistribution is permitted only in its unaltered
93** state. The ERFA version is not subject to this restriction and
94** therefore can be included in distributions which do not support the
95** concept of "read only" software.
96**
97** Although the intent is to replicate the SOFA API (other than
98** replacement of prefix names) and results (with the exception of
99** bugs; any that are discovered will be fixed), SOFA is not
100** responsible for any errors found in this version of the library.
101**
102** If you wish to acknowledge the SOFA heritage, please acknowledge
103** that you are using a library derived from SOFA, rather than SOFA
104** itself.
105**
106**
107** TERMS AND CONDITIONS
108**
109** Redistribution and use in source and binary forms, with or without
110** modification, are permitted provided that the following conditions
111** are met:
112**
113** 1 Redistributions of source code must retain the above copyright
114** notice, this list of conditions and the following disclaimer.
115**
116** 2 Redistributions in binary form must reproduce the above copyright
117** notice, this list of conditions and the following disclaimer in
118** the documentation and/or other materials provided with the
119** distribution.
120**
121** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
122** the International Astronomical Union nor the names of its
123** contributors may be used to endorse or promote products derived
124** from this software without specific prior written permission.
125**
126** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
127** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
128** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
129** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
130** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
131** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
132** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
133** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
134** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
135** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
136** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
137** POSSIBILITY OF SUCH DAMAGE.
138**
139*/
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