source: trunk/FACT++/erfa/src/gmst00.c@ 18614

Last change on this file since 18614 was 18348, checked in by tbretz, 9 years ago
File size: 6.1 KB
Line 
1#include "erfa.h"
2
3double eraGmst00(double uta, double utb, double tta, double ttb)
4/*
5** - - - - - - - - - -
6** e r a G m s t 0 0
7** - - - - - - - - - -
8**
9** Greenwich mean sidereal time (model consistent with IAU 2000
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 mean 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. If UT1 is used for
46** both purposes, errors of order 100 microarcseconds result.
47**
48** 3) This GMST is compatible with the IAU 2000 resolutions and must be
49** used only in conjunction with other IAU 2000 compatible
50** components such as precession-nutation and equation of the
51** equinoxes.
52**
53** 4) The result is returned in the range 0 to 2pi.
54**
55** 5) The algorithm is from Capitaine et al. (2003) and IERS
56** Conventions 2003.
57**
58** Called:
59** eraEra00 Earth rotation angle, IAU 2000
60** eraAnp normalize angle into range 0 to 2pi
61**
62** References:
63**
64** Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to
65** implement the IAU 2000 definition of UT1", Astronomy &
66** Astrophysics, 406, 1135-1149 (2003)
67**
68** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
69** IERS Technical Note No. 32, BKG (2004)
70**
71** Copyright (C) 2013-2015, NumFOCUS Foundation.
72** Derived, with permission, from the SOFA library. See notes at end of file.
73*/
74{
75 double t, gmst;
76
77/* TT Julian centuries since J2000.0. */
78 t = ((tta - ERFA_DJ00) + ttb) / ERFA_DJC;
79
80/* Greenwich Mean Sidereal Time, IAU 2000. */
81 gmst = eraAnp(eraEra00(uta, utb) +
82 ( 0.014506 +
83 ( 4612.15739966 +
84 ( 1.39667721 +
85 ( -0.00009344 +
86 ( 0.00001882 )
87 * t) * t) * t) * t) * ERFA_DAS2R);
88
89 return gmst;
90
91}
92/*----------------------------------------------------------------------
93**
94**
95** Copyright (C) 2013-2015, NumFOCUS Foundation.
96** All rights reserved.
97**
98** This library is derived, with permission, from the International
99** Astronomical Union's "Standards of Fundamental Astronomy" library,
100** available from http://www.iausofa.org.
101**
102** The ERFA version is intended to retain identical functionality to
103** the SOFA library, but made distinct through different function and
104** file names, as set out in the SOFA license conditions. The SOFA
105** original has a role as a reference standard for the IAU and IERS,
106** and consequently redistribution is permitted only in its unaltered
107** state. The ERFA version is not subject to this restriction and
108** therefore can be included in distributions which do not support the
109** concept of "read only" software.
110**
111** Although the intent is to replicate the SOFA API (other than
112** replacement of prefix names) and results (with the exception of
113** bugs; any that are discovered will be fixed), SOFA is not
114** responsible for any errors found in this version of the library.
115**
116** If you wish to acknowledge the SOFA heritage, please acknowledge
117** that you are using a library derived from SOFA, rather than SOFA
118** itself.
119**
120**
121** TERMS AND CONDITIONS
122**
123** Redistribution and use in source and binary forms, with or without
124** modification, are permitted provided that the following conditions
125** are met:
126**
127** 1 Redistributions of source code must retain the above copyright
128** notice, this list of conditions and the following disclaimer.
129**
130** 2 Redistributions in binary form must reproduce the above copyright
131** notice, this list of conditions and the following disclaimer in
132** the documentation and/or other materials provided with the
133** distribution.
134**
135** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
136** the International Astronomical Union nor the names of its
137** contributors may be used to endorse or promote products derived
138** from this software without specific prior written permission.
139**
140** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
141** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
142** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
143** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
144** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
145** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
146** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
147** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
148** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
149** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
150** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
151** POSSIBILITY OF SUCH DAMAGE.
152**
153*/
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