| 1 | #include "slalib.h"
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| 2 | #include "slamac.h"
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| 3 | void slaDav2m ( double axvec[3], double rmat[3][3] )
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| 4 | /*
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| 5 | ** - - - - - - - - -
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| 6 | ** s l a D a v 2 m
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| 7 | ** - - - - - - - - -
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| 8 | **
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| 9 | ** Form the rotation matrix corresponding to a given axial vector.
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| 10 | **
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| 11 | ** (double precision)
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| 12 | **
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| 13 | ** A rotation matrix describes a rotation about some arbitrary axis.
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| 14 | ** The axis is called the Euler axis, and the angle through which the
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| 15 | ** reference frame rotates is called the Euler angle. The axial
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| 16 | ** vector supplied to this routine has the same direction as the
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| 17 | ** Euler axis, and its magnitude is the Euler angle in radians.
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| 18 | **
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| 19 | ** Given:
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| 20 | ** axvec double[3] axial vector (radians)
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| 21 | **
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| 22 | ** Returned:
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| 23 | ** rmat double[3][3] rotation matrix
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| 24 | **
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| 25 | ** If axvec is null, the unit matrix is returned.
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| 26 | **
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| 27 | ** The reference frame rotates clockwise as seen looking along
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| 28 | ** the axial vector from the origin.
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| 29 | **
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| 30 | ** Last revision: 25 July 1993
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| 31 | **
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| 32 | ** Copyright P.T.Wallace. All rights reserved.
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| 33 | */
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| 34 | {
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| 35 | double x, y, z, phi, s, c, w;
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| 36 |
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| 37 | /* Euler angle - magnitude of axial vector - and functions */
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| 38 | x = axvec[0];
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| 39 | y = axvec[1];
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| 40 | z = axvec[2];
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| 41 | phi = sqrt ( x * x + y * y + z * z );
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| 42 | s = sin ( phi );
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| 43 | c = cos ( phi );
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| 44 | w = 1.0 - c;
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| 45 |
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| 46 | /* Euler axis - direction of axial vector (perhaps null) */
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| 47 | if ( phi != 0.0 ) {
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| 48 | x = x / phi;
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| 49 | y = y / phi;
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| 50 | z = z / phi;
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| 51 | }
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| 52 |
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| 53 | /* Compute the rotation matrix */
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| 54 | rmat[0][0] = x * x * w + c;
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| 55 | rmat[0][1] = x * y * w + z * s;
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| 56 | rmat[0][2] = x * z * w - y * s;
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| 57 | rmat[1][0] = x * y * w - z * s;
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| 58 | rmat[1][1] = y * y * w + c;
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| 59 | rmat[1][2] = y * z * w + x * s;
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| 60 | rmat[2][0] = x * z * w + y * s;
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| 61 | rmat[2][1] = y * z * w - x * s;
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| 62 | rmat[2][2] = z * z * w + c;
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| 63 | }
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