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

Last change on this file since 18679 was 18348, checked in by tbretz, 9 years ago
File size: 4.1 KB
Line 
1#include "erfa.h"
2
3double eraPas(double al, double ap, double bl, double bp)
4/*
5** - - - - - - -
6** e r a P a s
7** - - - - - - -
8**
9** Position-angle from spherical coordinates.
10**
11** Given:
12** al double longitude of point A (e.g. RA) in radians
13** ap double latitude of point A (e.g. Dec) in radians
14** bl double longitude of point B
15** bp double latitude of point B
16**
17** Returned (function value):
18** double position angle of B with respect to A
19**
20** Notes:
21**
22** 1) The result is the bearing (position angle), in radians, of point
23** B with respect to point A. It is in the range -pi to +pi. The
24** sense is such that if B is a small distance "east" of point A,
25** the bearing is approximately +pi/2.
26**
27** 2) Zero is returned if the two points are coincident.
28**
29** Copyright (C) 2013-2015, NumFOCUS Foundation.
30** Derived, with permission, from the SOFA library. See notes at end of file.
31*/
32{
33 double dl, x, y, pa;
34
35 dl = bl - al;
36 y = sin(dl) * cos(bp);
37 x = sin(bp) * cos(ap) - cos(bp) * sin(ap) * cos(dl);
38 pa = ((x != 0.0) || (y != 0.0)) ? atan2(y, x) : 0.0;
39
40 return pa;
41
42}
43/*----------------------------------------------------------------------
44**
45**
46** Copyright (C) 2013-2015, NumFOCUS Foundation.
47** All rights reserved.
48**
49** This library is derived, with permission, from the International
50** Astronomical Union's "Standards of Fundamental Astronomy" library,
51** available from http://www.iausofa.org.
52**
53** The ERFA version is intended to retain identical functionality to
54** the SOFA library, but made distinct through different function and
55** file names, as set out in the SOFA license conditions. The SOFA
56** original has a role as a reference standard for the IAU and IERS,
57** and consequently redistribution is permitted only in its unaltered
58** state. The ERFA version is not subject to this restriction and
59** therefore can be included in distributions which do not support the
60** concept of "read only" software.
61**
62** Although the intent is to replicate the SOFA API (other than
63** replacement of prefix names) and results (with the exception of
64** bugs; any that are discovered will be fixed), SOFA is not
65** responsible for any errors found in this version of the library.
66**
67** If you wish to acknowledge the SOFA heritage, please acknowledge
68** that you are using a library derived from SOFA, rather than SOFA
69** itself.
70**
71**
72** TERMS AND CONDITIONS
73**
74** Redistribution and use in source and binary forms, with or without
75** modification, are permitted provided that the following conditions
76** are met:
77**
78** 1 Redistributions of source code must retain the above copyright
79** notice, this list of conditions and the following disclaimer.
80**
81** 2 Redistributions in binary form must reproduce the above copyright
82** notice, this list of conditions and the following disclaimer in
83** the documentation and/or other materials provided with the
84** distribution.
85**
86** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
87** the International Astronomical Union nor the names of its
88** contributors may be used to endorse or promote products derived
89** from this software without specific prior written permission.
90**
91** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
92** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
93** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
94** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
95** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
96** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
97** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
98** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
99** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
100** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
101** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
102** POSSIBILITY OF SUCH DAMAGE.
103**
104*/
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