source: trunk/FACT++/erfa/src/sepp.c

Last change on this file was 18921, checked in by tbretz, 7 years ago
Updated to ERFA 1.4.0
File size: 4.3 KB
Line 
1#include "erfa.h"
2
3double eraSepp(double a[3], double b[3])
4/*
5** - - - - - - - -
6** e r a S e p p
7** - - - - - - - -
8**
9** Angular separation between two p-vectors.
10**
11** Given:
12** a double[3] first p-vector (not necessarily unit length)
13** b double[3] second p-vector (not necessarily unit length)
14**
15** Returned (function value):
16** double angular separation (radians, always positive)
17**
18** Notes:
19**
20** 1) If either vector is null, a zero result is returned.
21**
22** 2) The angular separation is most simply formulated in terms of
23** scalar product. However, this gives poor accuracy for angles
24** near zero and pi. The present algorithm uses both cross product
25** and dot product, to deliver full accuracy whatever the size of
26** the angle.
27**
28** Called:
29** eraPxp vector product of two p-vectors
30** eraPm modulus of p-vector
31** eraPdp scalar product of two p-vectors
32**
33** Copyright (C) 2013-2017, NumFOCUS Foundation.
34** Derived, with permission, from the SOFA library. See notes at end of file.
35*/
36{
37 double axb[3], ss, cs, s;
38
39
40/* Sine of angle between the vectors, multiplied by the two moduli. */
41 eraPxp(a, b, axb);
42 ss = eraPm(axb);
43
44/* Cosine of the angle, multiplied by the two moduli. */
45 cs = eraPdp(a, b);
46
47/* The angle. */
48 s = ((ss != 0.0) || (cs != 0.0)) ? atan2(ss, cs) : 0.0;
49
50 return s;
51
52}
53/*----------------------------------------------------------------------
54**
55**
56** Copyright (C) 2013-2017, NumFOCUS Foundation.
57** All rights reserved.
58**
59** This library is derived, with permission, from the International
60** Astronomical Union's "Standards of Fundamental Astronomy" library,
61** available from http://www.iausofa.org.
62**
63** The ERFA version is intended to retain identical functionality to
64** the SOFA library, but made distinct through different function and
65** file names, as set out in the SOFA license conditions. The SOFA
66** original has a role as a reference standard for the IAU and IERS,
67** and consequently redistribution is permitted only in its unaltered
68** state. The ERFA version is not subject to this restriction and
69** therefore can be included in distributions which do not support the
70** concept of "read only" software.
71**
72** Although the intent is to replicate the SOFA API (other than
73** replacement of prefix names) and results (with the exception of
74** bugs; any that are discovered will be fixed), SOFA is not
75** responsible for any errors found in this version of the library.
76**
77** If you wish to acknowledge the SOFA heritage, please acknowledge
78** that you are using a library derived from SOFA, rather than SOFA
79** itself.
80**
81**
82** TERMS AND CONDITIONS
83**
84** Redistribution and use in source and binary forms, with or without
85** modification, are permitted provided that the following conditions
86** are met:
87**
88** 1 Redistributions of source code must retain the above copyright
89** notice, this list of conditions and the following disclaimer.
90**
91** 2 Redistributions in binary form must reproduce the above copyright
92** notice, this list of conditions and the following disclaimer in
93** the documentation and/or other materials provided with the
94** distribution.
95**
96** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
97** the International Astronomical Union nor the names of its
98** contributors may be used to endorse or promote products derived
99** from this software without specific prior written permission.
100**
101** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
102** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
103** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
104** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
105** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
106** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
107** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
108** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
109** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
110** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
111** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
112** POSSIBILITY OF SUCH DAMAGE.
113**
114*/
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