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Diffstat (limited to 'ast/erfa/ldn.c')
| -rw-r--r-- | ast/erfa/ldn.c | 183 |
1 files changed, 183 insertions, 0 deletions
diff --git a/ast/erfa/ldn.c b/ast/erfa/ldn.c new file mode 100644 index 0000000..5ad0a50 --- /dev/null +++ b/ast/erfa/ldn.c @@ -0,0 +1,183 @@ +#include "erfa.h" + +void eraLdn(int n, eraLDBODY b[], double ob[3], double sc[3], + double sn[3]) +/*+ +** - - - - - - - +** e r a L d n +** - - - - - - - +** +** For a star, apply light deflection by multiple solar-system bodies, +** as part of transforming coordinate direction into natural direction. +** +** Given: +** n int number of bodies (note 1) +** b eraLDBODY[n] data for each of the n bodies (Notes 1,2): +** bm double mass of the body (solar masses, Note 3) +** dl double deflection limiter (Note 4) +** pv [2][3] barycentric PV of the body (au, au/day) +** ob double[3] barycentric position of the observer (au) +** sc double[3] observer to star coord direction (unit vector) +** +** Returned: +** sn double[3] observer to deflected star (unit vector) +** +** 1) The array b contains n entries, one for each body to be +** considered. If n = 0, no gravitational light deflection will be +** applied, not even for the Sun. +** +** 2) The array b should include an entry for the Sun as well as for +** any planet or other body to be taken into account. The entries +** should be in the order in which the light passes the body. +** +** 3) In the entry in the b array for body i, the mass parameter +** b[i].bm can, as required, be adjusted in order to allow for such +** effects as quadrupole field. +** +** 4) The deflection limiter parameter b[i].dl is phi^2/2, where phi is +** the angular separation (in radians) between star and body at +** which limiting is applied. As phi shrinks below the chosen +** threshold, the deflection is artificially reduced, reaching zero +** for phi = 0. Example values suitable for a terrestrial +** observer, together with masses, are as follows: +** +** body i b[i].bm b[i].dl +** +** Sun 1.0 6e-6 +** Jupiter 0.00095435 3e-9 +** Saturn 0.00028574 3e-10 +** +** 5) For cases where the starlight passes the body before reaching the +** observer, the body is placed back along its barycentric track by +** the light time from that point to the observer. For cases where +** the body is "behind" the observer no such shift is applied. If +** a different treatment is preferred, the user has the option of +** instead using the eraLd function. Similarly, eraLd can be used +** for cases where the source is nearby, not a star. +** +** 6) The returned vector sn is not normalized, but the consequential +** departure from unit magnitude is always negligible. +** +** 7) The arguments sc and sn can be the same array. +** +** 8) For efficiency, validation is omitted. The supplied masses must +** be greater than zero, the position and velocity vectors must be +** right, and the deflection limiter greater than zero. +** +** Reference: +** +** Urban, S. & Seidelmann, P. K. (eds), Explanatory Supplement to +** the Astronomical Almanac, 3rd ed., University Science Books +** (2013), Section 7.2.4. +** +** Called: +** eraCp copy p-vector +** eraPdp scalar product of two p-vectors +** eraPmp p-vector minus p-vector +** eraPpsp p-vector plus scaled p-vector +** eraPn decompose p-vector into modulus and direction +** eraLd light deflection by a solar-system body +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ +/* Light time for 1 AU (days) */ + const double CR = ERFA_AULT/ERFA_DAYSEC; + + int i; + double v[3], dt, ev[3], em, e[3]; + + +/* Star direction prior to deflection. */ + eraCp(sc, sn); + +/* Body by body. */ + for ( i = 0; i < n; i++ ) { + + /* Body to observer vector at epoch of observation (au). */ + eraPmp ( ob, b[i].pv[0], v ); + + /* Minus the time since the light passed the body (days). */ + dt = eraPdp(sn,v) * CR; + + /* Neutralize if the star is "behind" the observer. */ + dt = ERFA_GMIN(dt, 0.0); + + /* Backtrack the body to the time the light was passing the body. */ + eraPpsp(v, -dt, b[i].pv[1], ev); + + /* Body to observer vector as magnitude and direction. */ + eraPn(ev, &em, e); + + /* Apply light deflection for this body. */ + eraLd ( b[i].bm, sn, sn, e, em, b[i].dl, sn ); + + /* Next body. */ + } + +/* 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. +** +*/ |