source: trunk/FACT++/sofa/src/ldn.c@ 18368

Last change on this file since 18368 was 18346, checked in by tbretz, 11 years ago
File size: 8.6 KB
Line 
1#include "sofa.h"
2
3void iauLdn(int n, iauLDBODY b[], double ob[3], double sc[3],
4 double sn[3])
5/*+
6** - - - - - - -
7** i a u L d n
8** - - - - - - -
9**
10** For a star, apply light deflection by multiple solar-system bodies,
11** as part of transforming coordinate direction into natural direction.
12**
13** This function is part of the International Astronomical Union's
14** SOFA (Standards of Fundamental Astronomy) software collection.
15**
16** Status: support function.
17**
18** Given:
19** n int number of bodies (note 1)
20** b iauLDBODY[n] data for each of the n bodies (Notes 1,2):
21** bm double mass of the body (solar masses, Note 3)
22** dl double deflection limiter (Note 4)
23** pv [2][3] barycentric PV of the body (au, au/day)
24** ob double[3] barycentric position of the observer (au)
25** sc double[3] observer to star coord direction (unit vector)
26**
27** Returned:
28** sn double[3] observer to deflected star (unit vector)
29**
30** 1) The array b contains n entries, one for each body to be
31** considered. If n = 0, no gravitational light deflection will be
32** applied, not even for the Sun.
33**
34** 2) The array b should include an entry for the Sun as well as for
35** any planet or other body to be taken into account. The entries
36** should be in the order in which the light passes the body.
37**
38** 3) In the entry in the b array for body i, the mass parameter
39** b[i].bm can, as required, be adjusted in order to allow for such
40** effects as quadrupole field.
41**
42** 4) The deflection limiter parameter b[i].dl is phi^2/2, where phi is
43** the angular separation (in radians) between star and body at
44** which limiting is applied. As phi shrinks below the chosen
45** threshold, the deflection is artificially reduced, reaching zero
46** for phi = 0. Example values suitable for a terrestrial
47** observer, together with masses, are as follows:
48**
49** body i b[i].bm b[i].dl
50**
51** Sun 1.0 6e-6
52** Jupiter 0.00095435 3e-9
53** Saturn 0.00028574 3e-10
54**
55** 5) For cases where the starlight passes the body before reaching the
56** observer, the body is placed back along its barycentric track by
57** the light time from that point to the observer. For cases where
58** the body is "behind" the observer no such shift is applied. If
59** a different treatment is preferred, the user has the option of
60** instead using the iauLd function. Similarly, iauLd can be used
61** for cases where the source is nearby, not a star.
62**
63** 6) The returned vector sn is not normalized, but the consequential
64** departure from unit magnitude is always negligible.
65**
66** 7) The arguments sc and sn can be the same array.
67**
68** 8) For efficiency, validation is omitted. The supplied masses must
69** be greater than zero, the position and velocity vectors must be
70** right, and the deflection limiter greater than zero.
71**
72** Reference:
73**
74** Urban, S. & Seidelmann, P. K. (eds), Explanatory Supplement to
75** the Astronomical Almanac, 3rd ed., University Science Books
76** (2013), Section 7.2.4.
77**
78** Called:
79** iauCp copy p-vector
80** iauPdp scalar product of two p-vectors
81** iauPmp p-vector minus p-vector
82** iauPpsp p-vector plus scaled p-vector
83** iauPn decompose p-vector into modulus and direction
84** iauLd light deflection by a solar-system body
85**
86** This revision: 2013 October 9
87**
88** SOFA release 2015-02-09
89**
90** Copyright (C) 2015 IAU SOFA Board. See notes at end.
91*/
92{
93/* Light time for 1 AU (days) */
94 const double CR = AULT/DAYSEC;
95
96 int i;
97 double v[3], dt, ev[3], em, e[3];
98
99/* Star direction prior to deflection. */
100 iauCp(sc, sn);
101
102/* Body by body. */
103 for ( i = 0; i < n; i++ ) {
104
105 /* Body to observer vector at epoch of observation (au). */
106 iauPmp ( ob, b[i].pv[0], v );
107
108 /* Minus the time since the light passed the body (days). */
109 dt = iauPdp(sn,v) * CR;
110
111 /* Neutralize if the star is "behind" the observer. */
112 dt = gmin(dt, 0.0);
113
114 /* Backtrack the body to the time the light was passing the body. */
115 iauPpsp(v, -dt, b[i].pv[1], ev);
116
117 /* Body to observer vector as magnitude and direction. */
118 iauPn(ev, &em, e);
119
120 /* Apply light deflection for this body. */
121 iauLd ( b[i].bm, sn, sn, e, em, b[i].dl, sn );
122
123 /* Next body. */
124 }
125
126/* Finished. */
127
128/*----------------------------------------------------------------------
129**
130** Copyright (C) 2015
131** Standards Of Fundamental Astronomy Board
132** of the International Astronomical Union.
133**
134** =====================
135** SOFA Software License
136** =====================
137**
138** NOTICE TO USER:
139**
140** BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
141** CONDITIONS WHICH APPLY TO ITS USE.
142**
143** 1. The Software is owned by the IAU SOFA Board ("SOFA").
144**
145** 2. Permission is granted to anyone to use the SOFA software for any
146** purpose, including commercial applications, free of charge and
147** without payment of royalties, subject to the conditions and
148** restrictions listed below.
149**
150** 3. You (the user) may copy and distribute SOFA source code to others,
151** and use and adapt its code and algorithms in your own software,
152** on a world-wide, royalty-free basis. That portion of your
153** distribution that does not consist of intact and unchanged copies
154** of SOFA source code files is a "derived work" that must comply
155** with the following requirements:
156**
157** a) Your work shall be marked or carry a statement that it
158** (i) uses routines and computations derived by you from
159** software provided by SOFA under license to you; and
160** (ii) does not itself constitute software provided by and/or
161** endorsed by SOFA.
162**
163** b) The source code of your derived work must contain descriptions
164** of how the derived work is based upon, contains and/or differs
165** from the original SOFA software.
166**
167** c) The names of all routines in your derived work shall not
168** include the prefix "iau" or "sofa" or trivial modifications
169** thereof such as changes of case.
170**
171** d) The origin of the SOFA components of your derived work must
172** not be misrepresented; you must not claim that you wrote the
173** original software, nor file a patent application for SOFA
174** software or algorithms embedded in the SOFA software.
175**
176** e) These requirements must be reproduced intact in any source
177** distribution and shall apply to anyone to whom you have
178** granted a further right to modify the source code of your
179** derived work.
180**
181** Note that, as originally distributed, the SOFA software is
182** intended to be a definitive implementation of the IAU standards,
183** and consequently third-party modifications are discouraged. All
184** variations, no matter how minor, must be explicitly marked as
185** such, as explained above.
186**
187** 4. You shall not cause the SOFA software to be brought into
188** disrepute, either by misuse, or use for inappropriate tasks, or
189** by inappropriate modification.
190**
191** 5. The SOFA software is provided "as is" and SOFA makes no warranty
192** as to its use or performance. SOFA does not and cannot warrant
193** the performance or results which the user may obtain by using the
194** SOFA software. SOFA makes no warranties, express or implied, as
195** to non-infringement of third party rights, merchantability, or
196** fitness for any particular purpose. In no event will SOFA be
197** liable to the user for any consequential, incidental, or special
198** damages, including any lost profits or lost savings, even if a
199** SOFA representative has been advised of such damages, or for any
200** claim by any third party.
201**
202** 6. The provision of any version of the SOFA software under the terms
203** and conditions specified herein does not imply that future
204** versions will also be made available under the same terms and
205** conditions.
206*
207** In any published work or commercial product which uses the SOFA
208** software directly, acknowledgement (see www.iausofa.org) is
209** appreciated.
210**
211** Correspondence concerning SOFA software should be addressed as
212** follows:
213**
214** By email: sofa@ukho.gov.uk
215** By post: IAU SOFA Center
216** HM Nautical Almanac Office
217** UK Hydrographic Office
218** Admiralty Way, Taunton
219** Somerset, TA1 2DN
220** United Kingdom
221**
222**--------------------------------------------------------------------*/
223
224}
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