diff options
Diffstat (limited to 'ast/erfa/sepp.c')
-rw-r--r-- | ast/erfa/sepp.c | 114 |
1 files changed, 114 insertions, 0 deletions
diff --git a/ast/erfa/sepp.c b/ast/erfa/sepp.c new file mode 100644 index 0000000..98f2671 --- /dev/null +++ b/ast/erfa/sepp.c @@ -0,0 +1,114 @@ +#include "erfa.h" + +double eraSepp(double a[3], double b[3]) +/* +** - - - - - - - - +** e r a S e p p +** - - - - - - - - +** +** Angular separation between two p-vectors. +** +** Given: +** a double[3] first p-vector (not necessarily unit length) +** b double[3] second p-vector (not necessarily unit length) +** +** Returned (function value): +** double angular separation (radians, always positive) +** +** Notes: +** +** 1) If either vector is null, a zero result is returned. +** +** 2) The angular separation is most simply formulated in terms of +** scalar product. However, this gives poor accuracy for angles +** near zero and pi. The present algorithm uses both cross product +** and dot product, to deliver full accuracy whatever the size of +** the angle. +** +** Called: +** eraPxp vector product of two p-vectors +** eraPm modulus of p-vector +** eraPdp scalar product of two p-vectors +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double axb[3], ss, cs, s; + + +/* Sine of angle between the vectors, multiplied by the two moduli. */ + eraPxp(a, b, axb); + ss = eraPm(axb); + +/* Cosine of the angle, multiplied by the two moduli. */ + cs = eraPdp(a, b); + +/* The angle. */ + s = ((ss != 0.0) || (cs != 0.0)) ? atan2(ss, cs) : 0.0; + + return s; + +} +/*---------------------------------------------------------------------- +** +** +** 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. +** +*/ |