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Diffstat (limited to 'ast/erfa/rm2v.c')
| -rw-r--r-- | ast/erfa/rm2v.c | 120 |
1 files changed, 120 insertions, 0 deletions
diff --git a/ast/erfa/rm2v.c b/ast/erfa/rm2v.c new file mode 100644 index 0000000..2de16ce --- /dev/null +++ b/ast/erfa/rm2v.c @@ -0,0 +1,120 @@ +#include "erfa.h" + +void eraRm2v(double r[3][3], double w[3]) +/* +** - - - - - - - - +** e r a R m 2 v +** - - - - - - - - +** +** Express an r-matrix as an r-vector. +** +** Given: +** r double[3][3] rotation matrix +** +** Returned: +** w double[3] rotation vector (Note 1) +** +** Notes: +** +** 1) A rotation matrix describes a rotation through some angle about +** some arbitrary axis called the Euler axis. The "rotation vector" +** returned by this function has the same direction as the Euler axis, +** and its magnitude is the angle in radians. (The magnitude and +** direction can be separated by means of the function eraPn.) +** +** 2) If r is null, so is the result. If r is not a rotation matrix +** the result is undefined; r must be proper (i.e. have a positive +** determinant) and real orthogonal (inverse = transpose). +** +** 3) The reference frame rotates clockwise as seen looking along +** the rotation vector from the origin. +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double x, y, z, s2, c2, phi, f; + + + x = r[1][2] - r[2][1]; + y = r[2][0] - r[0][2]; + z = r[0][1] - r[1][0]; + s2 = sqrt(x*x + y*y + z*z); + if (s2 > 0) { + c2 = r[0][0] + r[1][1] + r[2][2] - 1.0; + phi = atan2(s2, c2); + f = phi / s2; + w[0] = x * f; + w[1] = y * f; + w[2] = z * f; + } else { + w[0] = 0.0; + w[1] = 0.0; + w[2] = 0.0; + } + + return; + +} +/*---------------------------------------------------------------------- +** +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** All rights reserved. +** +** This library is derived, with permission, from the International +** Astronomical Union's "Standards of Fundamental Astronomy" library, +** available from http://www.iausofa.org. +** +** The ERFA version is intended to retain identical functionality to +** the SOFA library, but made distinct through different function and +** file names, as set out in the SOFA license conditions. The SOFA +** original has a role as a reference standard for the IAU and IERS, +** and consequently redistribution is permitted only in its unaltered +** state. The ERFA version is not subject to this restriction and +** therefore can be included in distributions which do not support the +** concept of "read only" software. +** +** Although the intent is to replicate the SOFA API (other than +** replacement of prefix names) and results (with the exception of +** bugs; any that are discovered will be fixed), SOFA is not +** responsible for any errors found in this version of the library. +** +** If you wish to acknowledge the SOFA heritage, please acknowledge +** that you are using a library derived from SOFA, rather than SOFA +** itself. +** +** +** TERMS AND CONDITIONS +** +** Redistribution and use in source and binary forms, with or without +** modification, are permitted provided that the following conditions +** are met: +** +** 1 Redistributions of source code must retain the above copyright +** notice, this list of conditions and the following disclaimer. +** +** 2 Redistributions in binary form must reproduce the above copyright +** notice, this list of conditions and the following disclaimer in +** the documentation and/or other materials provided with the +** distribution. +** +** 3 Neither the name of the Standards Of Fundamental Astronomy Board, +** the International Astronomical Union nor the names of its +** contributors may be used to endorse or promote products derived +** from this software without specific prior written permission. +** +** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS +** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE +** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, +** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, +** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; +** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER +** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN +** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE +** POSSIBILITY OF SUCH DAMAGE. +** +*/ |