#include "sofa.h" int iauTpxes(double a, double b, double a0, double b0, double *xi, double *eta) /* ** - - - - - - - - - ** i a u T p x e s ** - - - - - - - - - ** ** In the tangent plane projection, given celestial spherical ** coordinates for a star and the tangent point, solve for the star's ** rectangular coordinates in the tangent plane. ** ** This function is part of the International Astronomical Union's ** SOFA (Standards of Fundamental Astronomy) software collection. ** ** Status: support function. ** ** Given: ** a,b double star's spherical coordinates ** a0,b0 double tangent point's spherical coordinates ** ** Returned: ** *xi,*eta double rectangular coordinates of star image (Note 2) ** ** Returned (function value): ** int status: 0 = OK ** 1 = star too far from axis ** 2 = antistar on tangent plane ** 3 = antistar too far from axis ** ** Notes: ** ** 1) The tangent plane projection is also called the "gnomonic ** projection" and the "central projection". ** ** 2) The eta axis points due north in the adopted coordinate system. ** If the spherical coordinates are observed (RA,Dec), the tangent ** plane coordinates (xi,eta) are conventionally called the ** "standard coordinates". For right-handed spherical coordinates, ** (xi,eta) are also right-handed. The units of (xi,eta) are, ** effectively, radians at the tangent point. ** ** 3) All angular arguments are in radians. ** ** 4) This function is a member of the following set: ** ** spherical vector solve for ** ** > iauTpxes < iauTpxev xi,eta ** iauTpsts iauTpstv star ** iauTpors iauTporv origin ** ** References: ** ** Calabretta M.R. & Greisen, E.W., 2002, "Representations of ** celestial coordinates in FITS", Astron.Astrophys. 395, 1077 ** ** Green, R.M., "Spherical Astronomy", Cambridge University Press, ** 1987, Chapter 13. ** ** This revision: 2018 January 2 ** ** SOFA release 2021-05-12 ** ** Copyright (C) 2021 IAU SOFA Board. See notes at end. */ { const double TINY = 1e-6; int j; double sb0, sb, cb0, cb, da, sda, cda, d; /* Functions of the spherical coordinates. */ sb0 = sin(b0); sb = sin(b); cb0 = cos(b0); cb = cos(b); da = a - a0; sda = sin(da); cda = cos(da); /* Reciprocal of star vector length to tangent plane. */ d = sb*sb0 + cb*cb0*cda; /* Check for error cases. */ if ( d > TINY ) { j = 0; } else if ( d >= 0.0 ) { j = 1; d = TINY; } else if ( d > -TINY ) { j = 2; d = -TINY; } else { j = 3; } /* Return the tangent plane coordinates (even in dubious cases). */ *xi = cb*sda / d; *eta = (sb*cb0 - cb*sb0*cda) / d; /* Return the status. */ return j; /* Finished. */ /*---------------------------------------------------------------------- ** ** 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 ** **--------------------------------------------------------------------*/ }