1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
|
SUBROUTINE sla_DM2AV (RMAT, AXVEC)
*+
* - - - - - -
* D M 2 A V
* - - - - - -
*
* From a rotation matrix, determine the corresponding axial vector.
* (double precision)
*
* A rotation matrix describes a rotation about some arbitrary axis.
* The axis is called the Euler axis, and the angle through which the
* reference frame rotates is called the Euler angle. The axial
* vector returned by this routine has the same direction as the
* Euler axis, and its magnitude is the Euler angle in radians. (The
* magnitude and direction can be separated by means of the routine
* sla_DVN.)
*
* Given:
* RMAT d(3,3) rotation matrix
*
* Returned:
* AXVEC d(3) axial vector (radians)
*
* The reference frame rotates clockwise as seen looking along
* the axial vector from the origin.
*
* If RMAT is null, so is the result.
*
* P.T.Wallace Starlink 24 December 1992
*
* Copyright (C) 1995 Rutherford Appleton Laboratory
*-
IMPLICIT NONE
DOUBLE PRECISION RMAT(3,3),AXVEC(3)
DOUBLE PRECISION X,Y,Z,S2,C2,PHI,F
X = RMAT(2,3)-RMAT(3,2)
Y = RMAT(3,1)-RMAT(1,3)
Z = RMAT(1,2)-RMAT(2,1)
S2 = SQRT(X*X+Y*Y+Z*Z)
IF (S2.NE.0D0) THEN
C2 = (RMAT(1,1)+RMAT(2,2)+RMAT(3,3)-1D0)
PHI = ATAN2(S2/2D0,C2/2D0)
F = PHI/S2
AXVEC(1) = X*F
AXVEC(2) = Y*F
AXVEC(3) = Z*F
ELSE
AXVEC(1) = 0D0
AXVEC(2) = 0D0
AXVEC(3) = 0D0
END IF
END
|
