source: trunk/FACT++/erfa/src/ldn.c@ 19098

Last change on this file since 19098 was 18921, checked in by tbretz, 7 years ago
Updated to ERFA 1.4.0
File size: 7.2 KB
Line 
1#include "erfa.h"
2
3void eraLdn(int n, eraLDBODY b[], double ob[3], double sc[3],
4 double sn[3])
5/*+
6** - - - - - - -
7** e r a 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** Given:
14** n int number of bodies (note 1)
15** b eraLDBODY[n] data for each of the n bodies (Notes 1,2):
16** bm double mass of the body (solar masses, Note 3)
17** dl double deflection limiter (Note 4)
18** pv [2][3] barycentric PV of the body (au, au/day)
19** ob double[3] barycentric position of the observer (au)
20** sc double[3] observer to star coord direction (unit vector)
21**
22** Returned:
23** sn double[3] observer to deflected star (unit vector)
24**
25** 1) The array b contains n entries, one for each body to be
26** considered. If n = 0, no gravitational light deflection will be
27** applied, not even for the Sun.
28**
29** 2) The array b should include an entry for the Sun as well as for
30** any planet or other body to be taken into account. The entries
31** should be in the order in which the light passes the body.
32**
33** 3) In the entry in the b array for body i, the mass parameter
34** b[i].bm can, as required, be adjusted in order to allow for such
35** effects as quadrupole field.
36**
37** 4) The deflection limiter parameter b[i].dl is phi^2/2, where phi is
38** the angular separation (in radians) between star and body at
39** which limiting is applied. As phi shrinks below the chosen
40** threshold, the deflection is artificially reduced, reaching zero
41** for phi = 0. Example values suitable for a terrestrial
42** observer, together with masses, are as follows:
43**
44** body i b[i].bm b[i].dl
45**
46** Sun 1.0 6e-6
47** Jupiter 0.00095435 3e-9
48** Saturn 0.00028574 3e-10
49**
50** 5) For cases where the starlight passes the body before reaching the
51** observer, the body is placed back along its barycentric track by
52** the light time from that point to the observer. For cases where
53** the body is "behind" the observer no such shift is applied. If
54** a different treatment is preferred, the user has the option of
55** instead using the eraLd function. Similarly, eraLd can be used
56** for cases where the source is nearby, not a star.
57**
58** 6) The returned vector sn is not normalized, but the consequential
59** departure from unit magnitude is always negligible.
60**
61** 7) The arguments sc and sn can be the same array.
62**
63** 8) For efficiency, validation is omitted. The supplied masses must
64** be greater than zero, the position and velocity vectors must be
65** right, and the deflection limiter greater than zero.
66**
67** Reference:
68**
69** Urban, S. & Seidelmann, P. K. (eds), Explanatory Supplement to
70** the Astronomical Almanac, 3rd ed., University Science Books
71** (2013), Section 7.2.4.
72**
73** Called:
74** eraCp copy p-vector
75** eraPdp scalar product of two p-vectors
76** eraPmp p-vector minus p-vector
77** eraPpsp p-vector plus scaled p-vector
78** eraPn decompose p-vector into modulus and direction
79** eraLd light deflection by a solar-system body
80**
81** Copyright (C) 2013-2017, NumFOCUS Foundation.
82** Derived, with permission, from the SOFA library. See notes at end of file.
83*/
84{
85/* Light time for 1 au (days) */
86 const double CR = ERFA_AULT/ERFA_DAYSEC;
87
88 int i;
89 double v[3], dt, ev[3], em, e[3];
90
91
92/* Star direction prior to deflection. */
93 eraCp(sc, sn);
94
95/* Body by body. */
96 for ( i = 0; i < n; i++ ) {
97
98 /* Body to observer vector at epoch of observation (au). */
99 eraPmp ( ob, b[i].pv[0], v );
100
101 /* Minus the time since the light passed the body (days). */
102 dt = eraPdp(sn,v) * CR;
103
104 /* Neutralize if the star is "behind" the observer. */
105 dt = ERFA_GMIN(dt, 0.0);
106
107 /* Backtrack the body to the time the light was passing the body. */
108 eraPpsp(v, -dt, b[i].pv[1], ev);
109
110 /* Body to observer vector as magnitude and direction. */
111 eraPn(ev, &em, e);
112
113 /* Apply light deflection for this body. */
114 eraLd ( b[i].bm, sn, sn, e, em, b[i].dl, sn );
115
116 /* Next body. */
117 }
118
119/* Finished. */
120
121}
122/*----------------------------------------------------------------------
123**
124**
125** Copyright (C) 2013-2017, NumFOCUS Foundation.
126** All rights reserved.
127**
128** This library is derived, with permission, from the International
129** Astronomical Union's "Standards of Fundamental Astronomy" library,
130** available from http://www.iausofa.org.
131**
132** The ERFA version is intended to retain identical functionality to
133** the SOFA library, but made distinct through different function and
134** file names, as set out in the SOFA license conditions. The SOFA
135** original has a role as a reference standard for the IAU and IERS,
136** and consequently redistribution is permitted only in its unaltered
137** state. The ERFA version is not subject to this restriction and
138** therefore can be included in distributions which do not support the
139** concept of "read only" software.
140**
141** Although the intent is to replicate the SOFA API (other than
142** replacement of prefix names) and results (with the exception of
143** bugs; any that are discovered will be fixed), SOFA is not
144** responsible for any errors found in this version of the library.
145**
146** If you wish to acknowledge the SOFA heritage, please acknowledge
147** that you are using a library derived from SOFA, rather than SOFA
148** itself.
149**
150**
151** TERMS AND CONDITIONS
152**
153** Redistribution and use in source and binary forms, with or without
154** modification, are permitted provided that the following conditions
155** are met:
156**
157** 1 Redistributions of source code must retain the above copyright
158** notice, this list of conditions and the following disclaimer.
159**
160** 2 Redistributions in binary form must reproduce the above copyright
161** notice, this list of conditions and the following disclaimer in
162** the documentation and/or other materials provided with the
163** distribution.
164**
165** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
166** the International Astronomical Union nor the names of its
167** contributors may be used to endorse or promote products derived
168** from this software without specific prior written permission.
169**
170** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
171** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
172** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
173** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
174** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
175** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
176** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
177** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
178** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
179** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
180** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
181** POSSIBILITY OF SUCH DAMAGE.
182**
183*/
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