source: branches/FACT++_lidctrl_new_eth/erfa/src/pas.c@ 19894

Last change on this file since 19894 was 18711, checked in by tbretz, 8 years ago
Updated to ERFA 1.3.0 (no relevant code change except the leap second at the beginning of 2017)
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) 2013-2016, 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
36 dl = bl - al;
37 y = sin(dl) * cos(bp);
38 x = sin(bp) * cos(ap) - cos(bp) * sin(ap) * cos(dl);
39 pa = ((x != 0.0) || (y != 0.0)) ? atan2(y, x) : 0.0;
40
41 return pa;
42
43}
44/*----------------------------------------------------------------------
45**
46**
47** Copyright (C) 2013-2016, NumFOCUS Foundation.
48** All rights reserved.
49**
50** This library is derived, with permission, from the International
51** Astronomical Union's "Standards of Fundamental Astronomy" library,
52** available from http://www.iausofa.org.
53**
54** The ERFA version is intended to retain identical functionality to
55** the SOFA library, but made distinct through different function and
56** file names, as set out in the SOFA license conditions. The SOFA
57** original has a role as a reference standard for the IAU and IERS,
58** and consequently redistribution is permitted only in its unaltered
59** state. The ERFA version is not subject to this restriction and
60** therefore can be included in distributions which do not support the
61** concept of "read only" software.
62**
63** Although the intent is to replicate the SOFA API (other than
64** replacement of prefix names) and results (with the exception of
65** bugs; any that are discovered will be fixed), SOFA is not
66** responsible for any errors found in this version of the library.
67**
68** If you wish to acknowledge the SOFA heritage, please acknowledge
69** that you are using a library derived from SOFA, rather than SOFA
70** itself.
71**
72**
73** TERMS AND CONDITIONS
74**
75** Redistribution and use in source and binary forms, with or without
76** modification, are permitted provided that the following conditions
77** are met:
78**
79** 1 Redistributions of source code must retain the above copyright
80** notice, this list of conditions and the following disclaimer.
81**
82** 2 Redistributions in binary form must reproduce the above copyright
83** notice, this list of conditions and the following disclaimer in
84** the documentation and/or other materials provided with the
85** distribution.
86**
87** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
88** the International Astronomical Union nor the names of its
89** contributors may be used to endorse or promote products derived
90** from this software without specific prior written permission.
91**
92** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
93** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
94** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
95** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
96** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
97** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
98** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
99** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
100** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
101** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
102** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
103** POSSIBILITY OF SUCH DAMAGE.
104**
105*/
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