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Diffstat (limited to 'ast/erfa/ld.c')
| -rw-r--r-- | ast/erfa/ld.c | 161 |
1 files changed, 161 insertions, 0 deletions
diff --git a/ast/erfa/ld.c b/ast/erfa/ld.c new file mode 100644 index 0000000..c1569fd --- /dev/null +++ b/ast/erfa/ld.c @@ -0,0 +1,161 @@ +#include "erfa.h" + +void eraLd(double bm, double p[3], double q[3], double e[3], + double em, double dlim, double p1[3]) +/* +** - - - - - - +** e r a L d +** - - - - - - +** +** Apply light deflection by a solar-system body, as part of +** transforming coordinate direction into natural direction. +** +** Given: +** bm double mass of the gravitating body (solar masses) +** p double[3] direction from observer to source (unit vector) +** q double[3] direction from body to source (unit vector) +** e double[3] direction from body to observer (unit vector) +** em double distance from body to observer (au) +** dlim double deflection limiter (Note 4) +** +** Returned: +** p1 double[3] observer to deflected source (unit vector) +** +** Notes: +** +** 1) The algorithm is based on Expr. (70) in Klioner (2003) and +** Expr. (7.63) in the Explanatory Supplement (Urban & Seidelmann +** 2013), with some rearrangement to minimize the effects of machine +** precision. +** +** 2) The mass parameter bm can, as required, be adjusted in order to +** allow for such effects as quadrupole field. +** +** 3) The barycentric position of the deflecting body should ideally +** correspond to the time of closest approach of the light ray to +** the body. +** +** 4) The deflection limiter parameter dlim is phi^2/2, where phi is +** the angular separation (in radians) between source and body at +** which limiting is applied. As phi shrinks below the chosen +** threshold, the deflection is artificially reduced, reaching zero +** for phi = 0. +** +** 5) The returned vector p1 is not normalized, but the consequential +** departure from unit magnitude is always negligible. +** +** 6) The arguments p and p1 can be the same array. +** +** 7) To accumulate total light deflection taking into account the +** contributions from several bodies, call the present function for +** each body in succession, in decreasing order of distance from the +** observer. +** +** 8) For efficiency, validation is omitted. The supplied vectors must +** be of unit magnitude, and the deflection limiter non-zero and +** positive. +** +** References: +** +** Urban, S. & Seidelmann, P. K. (eds), Explanatory Supplement to +** the Astronomical Almanac, 3rd ed., University Science Books +** (2013). +** +** Klioner, Sergei A., "A practical relativistic model for micro- +** arcsecond astrometry in space", Astr. J. 125, 1580-1597 (2003). +** +** Called: +** eraPdp scalar product of two p-vectors +** eraPxp vector product of two p-vectors +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + int i; + double qpe[3], qdqpe, w, eq[3], peq[3]; + + +/* q . (q + e). */ + for (i = 0; i < 3; i++) { + qpe[i] = q[i] + e[i]; + } + qdqpe = eraPdp(q, qpe); + +/* 2 x G x bm / ( em x c^2 x ( q . (q + e) ) ). */ + w = bm * ERFA_SRS / em / ERFA_GMAX(qdqpe,dlim); + +/* p x (e x q). */ + eraPxp(e, q, eq); + eraPxp(p, eq, peq); + +/* Apply the deflection. */ + for (i = 0; i < 3; i++) { + p1[i] = p[i] + w*peq[i]; + } + +/* Finished. */ + +} +/*---------------------------------------------------------------------- +** +** +** 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. +** +*/ |