source: trunk/FACT++/erfa/src/gst06.c@ 18679

Last change on this file since 18679 was 18348, checked in by tbretz, 9 years ago
File size: 5.9 KB
Line 
1#include "erfa.h"
2
3double eraGst06(double uta, double utb, double tta, double ttb,
4 double rnpb[3][3])
5/*
6** - - - - - - - - -
7** e r a G s t 0 6
8** - - - - - - - - -
9**
10** Greenwich apparent sidereal time, IAU 2006, given the NPB matrix.
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** rnpb double[3][3] nutation x precession x bias matrix
16**
17** Returned (function value):
18** double Greenwich apparent sidereal time (radians)
19**
20** Notes:
21**
22** 1) The UT1 and TT dates uta+utb and tta+ttb respectively, are both
23** Julian Dates, apportioned in any convenient way between the
24** argument pairs. For example, JD=2450123.7 could be expressed in
25** any of these ways, among others:
26**
27** Part A Part B
28**
29** 2450123.7 0.0 (JD method)
30** 2451545.0 -1421.3 (J2000 method)
31** 2400000.5 50123.2 (MJD method)
32** 2450123.5 0.2 (date & time method)
33**
34** The JD method is the most natural and convenient to use in
35** cases where the loss of several decimal digits of resolution
36** is acceptable (in the case of UT; the TT is not at all critical
37** in this respect). The J2000 and MJD methods are good compromises
38** between resolution and convenience. For UT, the date & time
39** method is best matched to the algorithm that is used by the Earth
40** rotation angle function, called internally: maximum precision is
41** delivered when the uta argument is for 0hrs UT1 on the day in
42** question and the utb argument lies in the range 0 to 1, or vice
43** versa.
44**
45** 2) Both UT1 and TT are required, UT1 to predict the Earth rotation
46** and TT to predict the effects of precession-nutation. If UT1 is
47** used for both purposes, errors of order 100 microarcseconds
48** result.
49**
50** 3) Although the function uses the IAU 2006 series for s+XY/2, it is
51** otherwise independent of the precession-nutation model and can in
52** practice be used with any equinox-based NPB matrix.
53**
54** 4) The result is returned in the range 0 to 2pi.
55**
56** Called:
57** eraBpn2xy extract CIP X,Y coordinates from NPB matrix
58** eraS06 the CIO locator s, given X,Y, IAU 2006
59** eraAnp normalize angle into range 0 to 2pi
60** eraEra00 Earth rotation angle, IAU 2000
61** eraEors equation of the origins, given NPB matrix and s
62**
63** Reference:
64**
65** Wallace, P.T. & Capitaine, N., 2006, Astron.Astrophys. 459, 981
66**
67** Copyright (C) 2013-2015, NumFOCUS Foundation.
68** Derived, with permission, from the SOFA library. See notes at end of file.
69*/
70{
71 double x, y, s, era, eors, gst;
72
73/* Extract CIP coordinates. */
74 eraBpn2xy(rnpb, &x, &y);
75
76/* The CIO locator, s. */
77 s = eraS06(tta, ttb, x, y);
78
79/* Greenwich apparent sidereal time. */
80 era = eraEra00(uta, utb);
81 eors = eraEors(rnpb, s);
82 gst = eraAnp(era - eors);
83
84 return gst;
85
86}
87/*----------------------------------------------------------------------
88**
89**
90** Copyright (C) 2013-2015, NumFOCUS Foundation.
91** All rights reserved.
92**
93** This library is derived, with permission, from the International
94** Astronomical Union's "Standards of Fundamental Astronomy" library,
95** available from http://www.iausofa.org.
96**
97** The ERFA version is intended to retain identical functionality to
98** the SOFA library, but made distinct through different function and
99** file names, as set out in the SOFA license conditions. The SOFA
100** original has a role as a reference standard for the IAU and IERS,
101** and consequently redistribution is permitted only in its unaltered
102** state. The ERFA version is not subject to this restriction and
103** therefore can be included in distributions which do not support the
104** concept of "read only" software.
105**
106** Although the intent is to replicate the SOFA API (other than
107** replacement of prefix names) and results (with the exception of
108** bugs; any that are discovered will be fixed), SOFA is not
109** responsible for any errors found in this version of the library.
110**
111** If you wish to acknowledge the SOFA heritage, please acknowledge
112** that you are using a library derived from SOFA, rather than SOFA
113** itself.
114**
115**
116** TERMS AND CONDITIONS
117**
118** Redistribution and use in source and binary forms, with or without
119** modification, are permitted provided that the following conditions
120** are met:
121**
122** 1 Redistributions of source code must retain the above copyright
123** notice, this list of conditions and the following disclaimer.
124**
125** 2 Redistributions in binary form must reproduce the above copyright
126** notice, this list of conditions and the following disclaimer in
127** the documentation and/or other materials provided with the
128** distribution.
129**
130** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
131** the International Astronomical Union nor the names of its
132** contributors may be used to endorse or promote products derived
133** from this software without specific prior written permission.
134**
135** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
136** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
137** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
138** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
139** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
140** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
141** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
142** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
143** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
144** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
145** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
146** POSSIBILITY OF SUCH DAMAGE.
147**
148*/
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