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 cond sub pod time 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) 2013-2019, 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             /* Note: the first constant, A, has to be adjusted by 12 hours */
74             /* because the UT1 is supplied as a Julian date, which begins */
75             /* at noon. */
76              
77             double d1, d2, t, f, gmst;
78              
79              
80             /* Julian centuries since fundamental epoch. */
81 0 0         if (dj1 < dj2) {
82             d1 = dj1;
83             d2 = dj2;
84             } else {
85             d1 = dj2;
86             d2 = dj1;
87             }
88 0           t = (d1 + (d2 - ERFA_DJ00)) / ERFA_DJC;
89              
90             /* Fractional part of JD(UT1), in seconds. */
91 0           f = ERFA_DAYSEC * (fmod(d1, 1.0) + fmod(d2, 1.0));
92              
93             /* GMST at this UT1. */
94 0           gmst = eraAnp(ERFA_DS2R * ((A + (B + (C + D * t) * t) * t) + f));
95              
96 0           return gmst;
97              
98             }
99             /*----------------------------------------------------------------------
100             **
101             **
102             ** Copyright (C) 2013-2019, NumFOCUS Foundation.
103             ** All rights reserved.
104             **
105             ** This library is derived, with permission, from the International
106             ** Astronomical Union's "Standards of Fundamental Astronomy" library,
107             ** available from http://www.iausofa.org.
108             **
109             ** The ERFA version is intended to retain identical functionality to
110             ** the SOFA library, but made distinct through different function and
111             ** file names, as set out in the SOFA license conditions. The SOFA
112             ** original has a role as a reference standard for the IAU and IERS,
113             ** and consequently redistribution is permitted only in its unaltered
114             ** state. The ERFA version is not subject to this restriction and
115             ** therefore can be included in distributions which do not support the
116             ** concept of "read only" software.
117             **
118             ** Although the intent is to replicate the SOFA API (other than
119             ** replacement of prefix names) and results (with the exception of
120             ** bugs; any that are discovered will be fixed), SOFA is not
121             ** responsible for any errors found in this version of the library.
122             **
123             ** If you wish to acknowledge the SOFA heritage, please acknowledge
124             ** that you are using a library derived from SOFA, rather than SOFA
125             ** itself.
126             **
127             **
128             ** TERMS AND CONDITIONS
129             **
130             ** Redistribution and use in source and binary forms, with or without
131             ** modification, are permitted provided that the following conditions
132             ** are met:
133             **
134             ** 1 Redistributions of source code must retain the above copyright
135             ** notice, this list of conditions and the following disclaimer.
136             **
137             ** 2 Redistributions in binary form must reproduce the above copyright
138             ** notice, this list of conditions and the following disclaimer in
139             ** the documentation and/or other materials provided with the
140             ** distribution.
141             **
142             ** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
143             ** the International Astronomical Union nor the names of its
144             ** contributors may be used to endorse or promote products derived
145             ** from this software without specific prior written permission.
146             **
147             ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
148             ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
149             ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
150             ** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
151             ** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
152             ** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
153             ** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
154             ** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
155             ** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
156             ** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
157             ** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
158             ** POSSIBILITY OF SUCH DAMAGE.
159             **
160             */