#include "sofa.h" double iauSepp(double a[3], double b[3]) /* ** - - - - - - - - ** i a u S e p p ** - - - - - - - - ** ** Angular separation between two p-vectors. ** ** This function is part of the International Astronomical Union's ** SOFA (Standards Of Fundamental Astronomy) software collection. ** ** Status: vector/matrix support function. ** ** 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: ** iauPxp vector product of two p-vectors ** iauPm modulus of p-vector ** iauPdp scalar product of two p-vectors ** ** This revision: 2013 June 18 ** ** SOFA release 2021-01-25 ** ** Copyright (C) 2021 IAU SOFA Board. See notes at end. */ { double axb[3], ss, cs, s; /* Sine of angle between the vectors, multiplied by the two moduli. */ iauPxp(a, b, axb); ss = iauPm(axb); /* Cosine of the angle, multiplied by the two moduli. */ cs = iauPdp(a, b); /* The angle. */ s = ((ss != 0.0) || (cs != 0.0)) ? atan2(ss, cs) : 0.0; return s; /*---------------------------------------------------------------------- ** ** Copyright (C) 2021 ** Standards Of Fundamental Astronomy Board ** of the International Astronomical Union. ** ** ===================== ** SOFA Software License ** ===================== ** ** NOTICE TO USER: ** ** BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND ** CONDITIONS WHICH APPLY TO ITS USE. ** ** 1. The Software is owned by the IAU SOFA Board ("SOFA"). ** ** 2. Permission is granted to anyone to use the SOFA software for any ** purpose, including commercial applications, free of charge and ** without payment of royalties, subject to the conditions and ** restrictions listed below. ** ** 3. You (the user) may copy and distribute SOFA source code to others, ** and use and adapt its code and algorithms in your own software, ** on a world-wide, royalty-free basis. That portion of your ** distribution that does not consist of intact and unchanged copies ** of SOFA source code files is a "derived work" that must comply ** with the following requirements: ** ** a) Your work shall be marked or carry a statement that it ** (i) uses routines and computations derived by you from ** software provided by SOFA under license to you; and ** (ii) does not itself constitute software provided by and/or ** endorsed by SOFA. ** ** b) The source code of your derived work must contain descriptions ** of how the derived work is based upon, contains and/or differs ** from the original SOFA software. ** ** c) The names of all routines in your derived work shall not ** include the prefix "iau" or "sofa" or trivial modifications ** thereof such as changes of case. ** ** d) The origin of the SOFA components of your derived work must ** not be misrepresented; you must not claim that you wrote the ** original software, nor file a patent application for SOFA ** software or algorithms embedded in the SOFA software. ** ** e) These requirements must be reproduced intact in any source ** distribution and shall apply to anyone to whom you have ** granted a further right to modify the source code of your ** derived work. ** ** Note that, as originally distributed, the SOFA software is ** intended to be a definitive implementation of the IAU standards, ** and consequently third-party modifications are discouraged. All ** variations, no matter how minor, must be explicitly marked as ** such, as explained above. ** ** 4. You shall not cause the SOFA software to be brought into ** disrepute, either by misuse, or use for inappropriate tasks, or ** by inappropriate modification. ** ** 5. The SOFA software is provided "as is" and SOFA makes no warranty ** as to its use or performance. SOFA does not and cannot warrant ** the performance or results which the user may obtain by using the ** SOFA software. SOFA makes no warranties, express or implied, as ** to non-infringement of third party rights, merchantability, or ** fitness for any particular purpose. In no event will SOFA be ** liable to the user for any consequential, incidental, or special ** damages, including any lost profits or lost savings, even if a ** SOFA representative has been advised of such damages, or for any ** claim by any third party. ** ** 6. The provision of any version of the SOFA software under the terms ** and conditions specified herein does not imply that future ** versions will also be made available under the same terms and ** conditions. * ** In any published work or commercial product which uses the SOFA ** software directly, acknowledgement (see www.iausofa.org) is ** appreciated. ** ** Correspondence concerning SOFA software should be addressed as ** follows: ** ** By email: sofa@ukho.gov.uk ** By post: IAU SOFA Center ** HM Nautical Almanac Office ** UK Hydrographic Office ** Admiralty Way, Taunton ** Somerset, TA1 2DN ** United Kingdom ** **--------------------------------------------------------------------*/ }