source: trunk/FACT++/erfa/src/sepp.c@ 18679

Last change on this file since 18679 was 18348, checked in by tbretz, 9 years ago
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) 2013-2015, 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/* Sine of angle between the vectors, multiplied by the two moduli. */
40 eraPxp(a, b, axb);
41 ss = eraPm(axb);
42
43/* Cosine of the angle, multiplied by the two moduli. */
44 cs = eraPdp(a, b);
45
46/* The angle. */
47 s = ((ss != 0.0) || (cs != 0.0)) ? atan2(ss, cs) : 0.0;
48
49 return s;
50
51}
52/*----------------------------------------------------------------------
53**
54**
55** Copyright (C) 2013-2015, NumFOCUS Foundation.
56** All rights reserved.
57**
58** This library is derived, with permission, from the International
59** Astronomical Union's "Standards of Fundamental Astronomy" library,
60** available from http://www.iausofa.org.
61**
62** The ERFA version is intended to retain identical functionality to
63** the SOFA library, but made distinct through different function and
64** file names, as set out in the SOFA license conditions. The SOFA
65** original has a role as a reference standard for the IAU and IERS,
66** and consequently redistribution is permitted only in its unaltered
67** state. The ERFA version is not subject to this restriction and
68** therefore can be included in distributions which do not support the
69** concept of "read only" software.
70**
71** Although the intent is to replicate the SOFA API (other than
72** replacement of prefix names) and results (with the exception of
73** bugs; any that are discovered will be fixed), SOFA is not
74** responsible for any errors found in this version of the library.
75**
76** If you wish to acknowledge the SOFA heritage, please acknowledge
77** that you are using a library derived from SOFA, rather than SOFA
78** itself.
79**
80**
81** TERMS AND CONDITIONS
82**
83** Redistribution and use in source and binary forms, with or without
84** modification, are permitted provided that the following conditions
85** are met:
86**
87** 1 Redistributions of source code must retain the above copyright
88** notice, this list of conditions and the following disclaimer.
89**
90** 2 Redistributions in binary form must reproduce the above copyright
91** notice, this list of conditions and the following disclaimer in
92** the documentation and/or other materials provided with the
93** distribution.
94**
95** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
96** the International Astronomical Union nor the names of its
97** contributors may be used to endorse or promote products derived
98** from this software without specific prior written permission.
99**
100** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
101** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
102** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
103** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
104** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
105** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
106** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
107** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
108** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
109** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
110** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
111** POSSIBILITY OF SUCH DAMAGE.
112**
113*/
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