source: branches/FACT++_part_filenames/erfa/src/era00.c@ 20115

Last change on this file since 20115 was 18711, checked in by tbretz, 9 years ago
Updated to ERFA 1.3.0 (no relevant code change except the leap second at the beginning of 2017)
File size: 5.4 KB
Line 
1#include "erfa.h"
2
3double eraEra00(double dj1, double dj2)
4/*
5** - - - - - - - - -
6** e r a E r a 0 0
7** - - - - - - - - -
8**
9** Earth rotation angle (IAU 2000 model).
10**
11** Given:
12** dj1,dj2 double UT1 as a 2-part Julian Date (see note)
13**
14** Returned (function value):
15** double Earth rotation angle (radians), range 0-2pi
16**
17** Notes:
18**
19** 1) The UT1 date dj1+dj2 is a Julian Date, apportioned in any
20** convenient way between the arguments dj1 and dj2. For example,
21** JD(UT1)=2450123.7 could be expressed in any of these ways,
22** among others:
23**
24** dj1 dj2
25**
26** 2450123.7 0.0 (JD method)
27** 2451545.0 -1421.3 (J2000 method)
28** 2400000.5 50123.2 (MJD method)
29** 2450123.5 0.2 (date & time method)
30**
31** The JD method is the most natural and convenient to use in
32** cases where the loss of several decimal digits of resolution
33** is acceptable. The J2000 and MJD methods are good compromises
34** between resolution and convenience. The date & time method is
35** best matched to the algorithm used: maximum precision is
36** delivered when the dj1 argument is for 0hrs UT1 on the day in
37** question and the dj2 argument lies in the range 0 to 1, or vice
38** versa.
39**
40** 2) The algorithm is adapted from Expression 22 of Capitaine et al.
41** 2000. The time argument has been expressed in days directly,
42** and, to retain precision, integer contributions have been
43** eliminated. The same formulation is given in IERS Conventions
44** (2003), Chap. 5, Eq. 14.
45**
46** Called:
47** eraAnp normalize angle into range 0 to 2pi
48**
49** References:
50**
51** Capitaine N., Guinot B. and McCarthy D.D, 2000, Astron.
52** Astrophys., 355, 398-405.
53**
54** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
55** IERS Technical Note No. 32, BKG (2004)
56**
57** Copyright (C) 2013-2016, NumFOCUS Foundation.
58** Derived, with permission, from the SOFA library. See notes at end of file.
59*/
60{
61 double d1, d2, t, f, theta;
62
63
64/* Days since fundamental epoch. */
65 if (dj1 < dj2) {
66 d1 = dj1;
67 d2 = dj2;
68 } else {
69 d1 = dj2;
70 d2 = dj1;
71 }
72 t = d1 + (d2- ERFA_DJ00);
73
74/* Fractional part of T (days). */
75 f = fmod(d1, 1.0) + fmod(d2, 1.0);
76
77/* Earth rotation angle at this UT1. */
78 theta = eraAnp(ERFA_D2PI * (f + 0.7790572732640
79 + 0.00273781191135448 * t));
80
81 return theta;
82
83}
84/*----------------------------------------------------------------------
85**
86**
87** Copyright (C) 2013-2016, NumFOCUS Foundation.
88** All rights reserved.
89**
90** This library is derived, with permission, from the International
91** Astronomical Union's "Standards of Fundamental Astronomy" library,
92** available from http://www.iausofa.org.
93**
94** The ERFA version is intended to retain identical functionality to
95** the SOFA library, but made distinct through different function and
96** file names, as set out in the SOFA license conditions. The SOFA
97** original has a role as a reference standard for the IAU and IERS,
98** and consequently redistribution is permitted only in its unaltered
99** state. The ERFA version is not subject to this restriction and
100** therefore can be included in distributions which do not support the
101** concept of "read only" software.
102**
103** Although the intent is to replicate the SOFA API (other than
104** replacement of prefix names) and results (with the exception of
105** bugs; any that are discovered will be fixed), SOFA is not
106** responsible for any errors found in this version of the library.
107**
108** If you wish to acknowledge the SOFA heritage, please acknowledge
109** that you are using a library derived from SOFA, rather than SOFA
110** itself.
111**
112**
113** TERMS AND CONDITIONS
114**
115** Redistribution and use in source and binary forms, with or without
116** modification, are permitted provided that the following conditions
117** are met:
118**
119** 1 Redistributions of source code must retain the above copyright
120** notice, this list of conditions and the following disclaimer.
121**
122** 2 Redistributions in binary form must reproduce the above copyright
123** notice, this list of conditions and the following disclaimer in
124** the documentation and/or other materials provided with the
125** distribution.
126**
127** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
128** the International Astronomical Union nor the names of its
129** contributors may be used to endorse or promote products derived
130** from this software without specific prior written permission.
131**
132** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
133** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
134** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
135** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
136** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
137** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
138** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
139** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
140** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
141** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
142** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
143** POSSIBILITY OF SUCH DAMAGE.
144**
145*/
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