source: trunk/FACT++/erfa/src/rm2v.c@ 18679

Last change on this file since 18679 was 18348, checked in by tbretz, 9 years ago
File size: 4.4 KB
Line 
1#include "erfa.h"
2
3void eraRm2v(double r[3][3], double w[3])
4/*
5** - - - - - - - -
6** e r a R m 2 v
7** - - - - - - - -
8**
9** Express an r-matrix as an r-vector.
10**
11** Given:
12** r double[3][3] rotation matrix
13**
14** Returned:
15** w double[3] rotation vector (Note 1)
16**
17** Notes:
18**
19** 1) A rotation matrix describes a rotation through some angle about
20** some arbitrary axis called the Euler axis. The "rotation vector"
21** returned by this function has the same direction as the Euler axis,
22** and its magnitude is the angle in radians. (The magnitude and
23** direction can be separated by means of the function eraPn.)
24**
25** 2) If r is null, so is the result. If r is not a rotation matrix
26** the result is undefined; r must be proper (i.e. have a positive
27** determinant) and real orthogonal (inverse = transpose).
28**
29** 3) The reference frame rotates clockwise as seen looking along
30** the rotation vector from the origin.
31**
32** Copyright (C) 2013-2015, NumFOCUS Foundation.
33** Derived, with permission, from the SOFA library. See notes at end of file.
34*/
35{
36 double x, y, z, s2, c2, phi, f;
37
38
39 x = r[1][2] - r[2][1];
40 y = r[2][0] - r[0][2];
41 z = r[0][1] - r[1][0];
42 s2 = sqrt(x*x + y*y + z*z);
43 if (s2 > 0) {
44 c2 = r[0][0] + r[1][1] + r[2][2] - 1.0;
45 phi = atan2(s2, c2);
46 f = phi / s2;
47 w[0] = x * f;
48 w[1] = y * f;
49 w[2] = z * f;
50 } else {
51 w[0] = 0.0;
52 w[1] = 0.0;
53 w[2] = 0.0;
54 }
55
56 return;
57
58}
59/*----------------------------------------------------------------------
60**
61**
62** Copyright (C) 2013-2015, NumFOCUS Foundation.
63** All rights reserved.
64**
65** This library is derived, with permission, from the International
66** Astronomical Union's "Standards of Fundamental Astronomy" library,
67** available from http://www.iausofa.org.
68**
69** The ERFA version is intended to retain identical functionality to
70** the SOFA library, but made distinct through different function and
71** file names, as set out in the SOFA license conditions. The SOFA
72** original has a role as a reference standard for the IAU and IERS,
73** and consequently redistribution is permitted only in its unaltered
74** state. The ERFA version is not subject to this restriction and
75** therefore can be included in distributions which do not support the
76** concept of "read only" software.
77**
78** Although the intent is to replicate the SOFA API (other than
79** replacement of prefix names) and results (with the exception of
80** bugs; any that are discovered will be fixed), SOFA is not
81** responsible for any errors found in this version of the library.
82**
83** If you wish to acknowledge the SOFA heritage, please acknowledge
84** that you are using a library derived from SOFA, rather than SOFA
85** itself.
86**
87**
88** TERMS AND CONDITIONS
89**
90** Redistribution and use in source and binary forms, with or without
91** modification, are permitted provided that the following conditions
92** are met:
93**
94** 1 Redistributions of source code must retain the above copyright
95** notice, this list of conditions and the following disclaimer.
96**
97** 2 Redistributions in binary form must reproduce the above copyright
98** notice, this list of conditions and the following disclaimer in
99** the documentation and/or other materials provided with the
100** distribution.
101**
102** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
103** the International Astronomical Union nor the names of its
104** contributors may be used to endorse or promote products derived
105** from this software without specific prior written permission.
106**
107** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
108** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
109** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
110** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
111** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
112** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
113** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
114** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
115** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
116** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
117** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
118** POSSIBILITY OF SUCH DAMAGE.
119**
120*/
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