File Coverage

erfasrc/src/gmst82.c

Criterion	Covered	Total	%
statement	0	6	0.0
branch	0	2	0.0
condition			n/a
subroutine			n/a
pod			n/a
total	0	8	0.0

line	stmt	bran	code
1			#include "erfa.h"
2
3	0		double eraGmst82(double dj1, double dj2)
4			/*
5			** - - - - - - - - - -
6			** e r a G m s t 8 2
7			** - - - - - - - - - -
8			**
9			** Universal Time to Greenwich mean sidereal time (IAU 1982 model).
10			**
11			** Given:
12			** dj1,dj2 double UT1 Julian Date (see note)
13			**
14			** Returned (function value):
15			** double Greenwich mean sidereal time (radians)
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 (JD method)
27			** 2451545 -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 accuracy (or, at
36			** least, minimum noise) is delivered when the dj1 argument is for
37			** 0hrs UT1 on the day in question and the dj2 argument lies in the
38			** range 0 to 1, or vice versa.
39			**
40			** 2) The algorithm is based on the IAU 1982 expression. This is
41			** always described as giving the GMST at 0 hours UT1. In fact, it
42			** gives the difference between the GMST and the UT, the steady
43			** 4-minutes-per-day drawing-ahead of ST with respect to UT. When
44			** whole days are ignored, the expression happens to equal the GMST
45			** at 0 hours UT1 each day.
46			**
47			** 3) In this function, the entire UT1 (the sum of the two arguments
48			** dj1 and dj2) is used directly as the argument for the standard
49			** formula, the constant term of which is adjusted by 12 hours to
50			** take account of the noon phasing of Julian Date. The UT1 is then
51			** added, but omitting whole days to conserve accuracy.
52			**
53			** Called:
54			** eraAnp normalize angle into range 0 to 2pi
55			**
56			** References:
57			**
58			** Transactions of the International Astronomical Union,
59			** XVIII B, 67 (1983).
60			**
61			** Aoki et al., Astron.Astrophys., 105, 359-361 (1982).
62			**
63			** Copyright (C) 2013-2020, NumFOCUS Foundation.
64			** Derived, with permission, from the SOFA library. See notes at end of file.
65			*/
66			{
67			/* Coefficients of IAU 1982 GMST-UT1 model */
68			double A = 24110.54841 - ERFA_DAYSEC / 2.0;
69			double B = 8640184.812866;
70			double C = 0.093104;
71			double D = -6.2e-6;
72
73			/* The first constant, A, has to be adjusted by 12 hours because the */
74			/* UT1 is supplied as a Julian date, which begins at noon. */
75
76			double d1, d2, t, f, gmst;
77
78
79			/* Julian centuries since fundamental epoch. */
80	0	0	if (dj1 < dj2) {
81			d1 = dj1;
82			d2 = dj2;
83			} else {
84			d1 = dj2;
85			d2 = dj1;
86			}
87	0		t = (d1 + (d2 - ERFA_DJ00)) / ERFA_DJC;
88
89			/* Fractional part of JD(UT1), in seconds. */
90	0		f = ERFA_DAYSEC * (fmod(d1, 1.0) + fmod(d2, 1.0));
91
92			/* GMST at this UT1. */
93	0		gmst = eraAnp(ERFA_DS2R * ((A + (B + (C + D * t) * t) * t) + f));
94
95	0		return gmst;
96
97			}
98			/*----------------------------------------------------------------------
99			**
100			**
101			** Copyright (C) 2013-2020, NumFOCUS Foundation.
102			** All rights reserved.
103			**
104			** This library is derived, with permission, from the International
105			** Astronomical Union's "Standards of Fundamental Astronomy" library,
106			** available from http://www.iausofa.org.
107			**
108			** The ERFA version is intended to retain identical functionality to
109			** the SOFA library, but made distinct through different function and
110			** file names, as set out in the SOFA license conditions. The SOFA
111			** original has a role as a reference standard for the IAU and IERS,
112			** and consequently redistribution is permitted only in its unaltered
113			** state. The ERFA version is not subject to this restriction and
114			** therefore can be included in distributions which do not support the
115			** concept of "read only" software.
116			**
117			** Although the intent is to replicate the SOFA API (other than
118			** replacement of prefix names) and results (with the exception of
119			** bugs; any that are discovered will be fixed), SOFA is not
120			** responsible for any errors found in this version of the library.
121			**
122			** If you wish to acknowledge the SOFA heritage, please acknowledge
123			** that you are using a library derived from SOFA, rather than SOFA
124			** itself.
125			**
126			**
127			** TERMS AND CONDITIONS
128			**
129			** Redistribution and use in source and binary forms, with or without
130			** modification, are permitted provided that the following conditions
131			** are met:
132			**
133			** 1 Redistributions of source code must retain the above copyright
134			** notice, this list of conditions and the following disclaimer.
135			**
136			** 2 Redistributions in binary form must reproduce the above copyright
137			** notice, this list of conditions and the following disclaimer in
138			** the documentation and/or other materials provided with the
139			** distribution.
140			**
141			** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
142			** the International Astronomical Union nor the names of its
143			** contributors may be used to endorse or promote products derived
144			** from this software without specific prior written permission.
145			**
146			** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
147			** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
148			** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
149			** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
150			** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
151			** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
152			** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
153			** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
154			** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
155			** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
156			** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
157			** POSSIBILITY OF SUCH DAMAGE.
158			**
159			*/