source: trunk/FACT++/sofa/src/starpv.c@ 18375

Last change on this file since 18375 was 18346, checked in by tbretz, 11 years ago
File size: 11.7 KB
Line 
1#include "sofa.h"
2
3int iauStarpv(double ra, double dec,
4 double pmr, double pmd, double px, double rv,
5 double pv[2][3])
6/*
7** - - - - - - - - - -
8** i a u S t a r p v
9** - - - - - - - - - -
10**
11** Convert star catalog coordinates to position+velocity vector.
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 (Note 1):
19** ra double right ascension (radians)
20** dec double declination (radians)
21** pmr double RA proper motion (radians/year)
22** pmd double Dec proper motion (radians/year)
23** px double parallax (arcseconds)
24** rv double radial velocity (km/s, positive = receding)
25**
26** Returned (Note 2):
27** pv double[2][3] pv-vector (AU, AU/day)
28**
29** Returned (function value):
30** int status:
31** 0 = no warnings
32** 1 = distance overridden (Note 6)
33** 2 = excessive speed (Note 7)
34** 4 = solution didn't converge (Note 8)
35** else = binary logical OR of the above
36**
37** Notes:
38**
39** 1) The star data accepted by this function are "observables" for an
40** imaginary observer at the solar-system barycenter. Proper motion
41** and radial velocity are, strictly, in terms of barycentric
42** coordinate time, TCB. For most practical applications, it is
43** permissible to neglect the distinction between TCB and ordinary
44** "proper" time on Earth (TT/TAI). The result will, as a rule, be
45** limited by the intrinsic accuracy of the proper-motion and
46** radial-velocity data; moreover, the pv-vector is likely to be
47** merely an intermediate result, so that a change of time unit
48** would cancel out overall.
49**
50** In accordance with normal star-catalog conventions, the object's
51** right ascension and declination are freed from the effects of
52** secular aberration. The frame, which is aligned to the catalog
53** equator and equinox, is Lorentzian and centered on the SSB.
54**
55** 2) The resulting position and velocity pv-vector is with respect to
56** the same frame and, like the catalog coordinates, is freed from
57** the effects of secular aberration. Should the "coordinate
58** direction", where the object was located at the catalog epoch, be
59** required, it may be obtained by calculating the magnitude of the
60** position vector pv[0][0-2] dividing by the speed of light in
61** AU/day to give the light-time, and then multiplying the space
62** velocity pv[1][0-2] by this light-time and adding the result to
63** pv[0][0-2].
64**
65** Summarizing, the pv-vector returned is for most stars almost
66** identical to the result of applying the standard geometrical
67** "space motion" transformation. The differences, which are the
68** subject of the Stumpff paper referenced below, are:
69**
70** (i) In stars with significant radial velocity and proper motion,
71** the constantly changing light-time distorts the apparent proper
72** motion. Note that this is a classical, not a relativistic,
73** effect.
74**
75** (ii) The transformation complies with special relativity.
76**
77** 3) Care is needed with units. The star coordinates are in radians
78** and the proper motions in radians per Julian year, but the
79** parallax is in arcseconds; the radial velocity is in km/s, but
80** the pv-vector result is in AU and AU/day.
81**
82** 4) The RA proper motion is in terms of coordinate angle, not true
83** angle. If the catalog uses arcseconds for both RA and Dec proper
84** motions, the RA proper motion will need to be divided by cos(Dec)
85** before use.
86**
87** 5) Straight-line motion at constant speed, in the inertial frame,
88** is assumed.
89**
90** 6) An extremely small (or zero or negative) parallax is interpreted
91** to mean that the object is on the "celestial sphere", the radius
92** of which is an arbitrary (large) value (see the constant PXMIN).
93** When the distance is overridden in this way, the status,
94** initially zero, has 1 added to it.
95**
96** 7) If the space velocity is a significant fraction of c (see the
97** constant VMAX), it is arbitrarily set to zero. When this action
98** occurs, 2 is added to the status.
99**
100** 8) The relativistic adjustment involves an iterative calculation.
101** If the process fails to converge within a set number (IMAX) of
102** iterations, 4 is added to the status.
103**
104** 9) The inverse transformation is performed by the function
105** iauPvstar.
106**
107** Called:
108** iauS2pv spherical coordinates to pv-vector
109** iauPm modulus of p-vector
110** iauZp zero p-vector
111** iauPn decompose p-vector into modulus and direction
112** iauPdp scalar product of two p-vectors
113** iauSxp multiply p-vector by scalar
114** iauPmp p-vector minus p-vector
115** iauPpp p-vector plus p-vector
116**
117** Reference:
118**
119** Stumpff, P., 1985, Astron.Astrophys. 144, 232-240.
120**
121** This revision: 2013 June 18
122**
123** SOFA release 2015-02-09
124**
125** Copyright (C) 2015 IAU SOFA Board. See notes at end.
126*/
127{
128/* Smallest allowed parallax */
129 static const double PXMIN = 1e-7;
130
131/* Largest allowed speed (fraction of c) */
132 static const double VMAX = 0.5;
133
134/* Maximum number of iterations for relativistic solution */
135 static const int IMAX = 100;
136
137 int i, iwarn;
138 double w, r, rd, rad, decd, v, x[3], usr[3], ust[3],
139 vsr, vst, betst, betsr, bett, betr,
140 dd, ddel, ur[3], ut[3],
141 d = 0.0, del = 0.0, /* to prevent */
142 odd = 0.0, oddel = 0.0, /* compiler */
143 od = 0.0, odel = 0.0; /* warnings */
144
145/* Distance (AU). */
146 if (px >= PXMIN) {
147 w = px;
148 iwarn = 0;
149 } else {
150 w = PXMIN;
151 iwarn = 1;
152 }
153 r = DR2AS / w;
154
155/* Radial velocity (AU/day). */
156 rd = DAYSEC * rv * 1e3 / DAU;
157
158/* Proper motion (radian/day). */
159 rad = pmr / DJY;
160 decd = pmd / DJY;
161
162/* To pv-vector (AU,AU/day). */
163 iauS2pv(ra, dec, r, rad, decd, rd, pv);
164
165/* If excessive velocity, arbitrarily set it to zero. */
166 v = iauPm(pv[1]);
167 if (v / DC > VMAX) {
168 iauZp(pv[1]);
169 iwarn += 2;
170 }
171
172/* Isolate the radial component of the velocity (AU/day). */
173 iauPn(pv[0], &w, x);
174 vsr = iauPdp(x, pv[1]);
175 iauSxp(vsr, x, usr);
176
177/* Isolate the transverse component of the velocity (AU/day). */
178 iauPmp(pv[1], usr, ust);
179 vst = iauPm(ust);
180
181/* Special-relativity dimensionless parameters. */
182 betsr = vsr / DC;
183 betst = vst / DC;
184
185/* Determine the inertial-to-observed relativistic correction terms. */
186 bett = betst;
187 betr = betsr;
188 for (i = 0; i < IMAX; i++) {
189 d = 1.0 + betr;
190 del = sqrt(1.0 - betr*betr - bett*bett) - 1.0;
191 betr = d * betsr + del;
192 bett = d * betst;
193 if (i > 0) {
194 dd = fabs(d - od);
195 ddel = fabs(del - odel);
196 if ((i > 1) && (dd >= odd) && (ddel >= oddel)) break;
197 odd = dd;
198 oddel = ddel;
199 }
200 od = d;
201 odel = del;
202 }
203 if (i >= IMAX) iwarn += 4;
204
205/* Replace observed radial velocity with inertial value. */
206 w = (betsr != 0.0) ? d + del / betsr : 1.0;
207 iauSxp(w, usr, ur);
208
209/* Replace observed tangential velocity with inertial value. */
210 iauSxp(d, ust, ut);
211
212/* Combine the two to obtain the inertial space velocity. */
213 iauPpp(ur, ut, pv[1]);
214
215/* Return the status. */
216 return iwarn;
217
218/*----------------------------------------------------------------------
219**
220** Copyright (C) 2015
221** Standards Of Fundamental Astronomy Board
222** of the International Astronomical Union.
223**
224** =====================
225** SOFA Software License
226** =====================
227**
228** NOTICE TO USER:
229**
230** BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
231** CONDITIONS WHICH APPLY TO ITS USE.
232**
233** 1. The Software is owned by the IAU SOFA Board ("SOFA").
234**
235** 2. Permission is granted to anyone to use the SOFA software for any
236** purpose, including commercial applications, free of charge and
237** without payment of royalties, subject to the conditions and
238** restrictions listed below.
239**
240** 3. You (the user) may copy and distribute SOFA source code to others,
241** and use and adapt its code and algorithms in your own software,
242** on a world-wide, royalty-free basis. That portion of your
243** distribution that does not consist of intact and unchanged copies
244** of SOFA source code files is a "derived work" that must comply
245** with the following requirements:
246**
247** a) Your work shall be marked or carry a statement that it
248** (i) uses routines and computations derived by you from
249** software provided by SOFA under license to you; and
250** (ii) does not itself constitute software provided by and/or
251** endorsed by SOFA.
252**
253** b) The source code of your derived work must contain descriptions
254** of how the derived work is based upon, contains and/or differs
255** from the original SOFA software.
256**
257** c) The names of all routines in your derived work shall not
258** include the prefix "iau" or "sofa" or trivial modifications
259** thereof such as changes of case.
260**
261** d) The origin of the SOFA components of your derived work must
262** not be misrepresented; you must not claim that you wrote the
263** original software, nor file a patent application for SOFA
264** software or algorithms embedded in the SOFA software.
265**
266** e) These requirements must be reproduced intact in any source
267** distribution and shall apply to anyone to whom you have
268** granted a further right to modify the source code of your
269** derived work.
270**
271** Note that, as originally distributed, the SOFA software is
272** intended to be a definitive implementation of the IAU standards,
273** and consequently third-party modifications are discouraged. All
274** variations, no matter how minor, must be explicitly marked as
275** such, as explained above.
276**
277** 4. You shall not cause the SOFA software to be brought into
278** disrepute, either by misuse, or use for inappropriate tasks, or
279** by inappropriate modification.
280**
281** 5. The SOFA software is provided "as is" and SOFA makes no warranty
282** as to its use or performance. SOFA does not and cannot warrant
283** the performance or results which the user may obtain by using the
284** SOFA software. SOFA makes no warranties, express or implied, as
285** to non-infringement of third party rights, merchantability, or
286** fitness for any particular purpose. In no event will SOFA be
287** liable to the user for any consequential, incidental, or special
288** damages, including any lost profits or lost savings, even if a
289** SOFA representative has been advised of such damages, or for any
290** claim by any third party.
291**
292** 6. The provision of any version of the SOFA software under the terms
293** and conditions specified herein does not imply that future
294** versions will also be made available under the same terms and
295** conditions.
296*
297** In any published work or commercial product which uses the SOFA
298** software directly, acknowledgement (see www.iausofa.org) is
299** appreciated.
300**
301** Correspondence concerning SOFA software should be addressed as
302** follows:
303**
304** By email: sofa@ukho.gov.uk
305** By post: IAU SOFA Center
306** HM Nautical Almanac Office
307** UK Hydrographic Office
308** Admiralty Way, Taunton
309** Somerset, TA1 2DN
310** United Kingdom
311**
312**--------------------------------------------------------------------*/
313}
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