source: trunk/FACT++/erfa/src/starpv.c@ 20035

Last change on this file since 20035 was 18921, checked in by tbretz, 9 years ago
Updated to ERFA 1.4.0
File size: 10.3 KB
Line 
1#include "erfa.h"
2
3int eraStarpv(double ra, double dec,
4 double pmr, double pmd, double px, double rv,
5 double pv[2][3])
6/*
7** - - - - - - - - - -
8** e r a S t a r p v
9** - - - - - - - - - -
10**
11** Convert star catalog coordinates to position+velocity vector.
12**
13** Given (Note 1):
14** ra double right ascension (radians)
15** dec double declination (radians)
16** pmr double RA proper motion (radians/year)
17** pmd double Dec proper motion (radians/year)
18** px double parallax (arcseconds)
19** rv double radial velocity (km/s, positive = receding)
20**
21** Returned (Note 2):
22** pv double[2][3] pv-vector (au, au/day)
23**
24** Returned (function value):
25** int status:
26** 0 = no warnings
27** 1 = distance overridden (Note 6)
28** 2 = excessive speed (Note 7)
29** 4 = solution didn't converge (Note 8)
30** else = binary logical OR of the above
31**
32** Notes:
33**
34** 1) The star data accepted by this function are "observables" for an
35** imaginary observer at the solar-system barycenter. Proper motion
36** and radial velocity are, strictly, in terms of barycentric
37** coordinate time, TCB. For most practical applications, it is
38** permissible to neglect the distinction between TCB and ordinary
39** "proper" time on Earth (TT/TAI). The result will, as a rule, be
40** limited by the intrinsic accuracy of the proper-motion and
41** radial-velocity data; moreover, the pv-vector is likely to be
42** merely an intermediate result, so that a change of time unit
43** would cancel out overall.
44**
45** In accordance with normal star-catalog conventions, the object's
46** right ascension and declination are freed from the effects of
47** secular aberration. The frame, which is aligned to the catalog
48** equator and equinox, is Lorentzian and centered on the SSB.
49**
50** 2) The resulting position and velocity pv-vector is with respect to
51** the same frame and, like the catalog coordinates, is freed from
52** the effects of secular aberration. Should the "coordinate
53** direction", where the object was located at the catalog epoch, be
54** required, it may be obtained by calculating the magnitude of the
55** position vector pv[0][0-2] dividing by the speed of light in
56** au/day to give the light-time, and then multiplying the space
57** velocity pv[1][0-2] by this light-time and adding the result to
58** pv[0][0-2].
59**
60** Summarizing, the pv-vector returned is for most stars almost
61** identical to the result of applying the standard geometrical
62** "space motion" transformation. The differences, which are the
63** subject of the Stumpff paper referenced below, are:
64**
65** (i) In stars with significant radial velocity and proper motion,
66** the constantly changing light-time distorts the apparent proper
67** motion. Note that this is a classical, not a relativistic,
68** effect.
69**
70** (ii) The transformation complies with special relativity.
71**
72** 3) Care is needed with units. The star coordinates are in radians
73** and the proper motions in radians per Julian year, but the
74** parallax is in arcseconds; the radial velocity is in km/s, but
75** the pv-vector result is in au and au/day.
76**
77** 4) The RA proper motion is in terms of coordinate angle, not true
78** angle. If the catalog uses arcseconds for both RA and Dec proper
79** motions, the RA proper motion will need to be divided by cos(Dec)
80** before use.
81**
82** 5) Straight-line motion at constant speed, in the inertial frame,
83** is assumed.
84**
85** 6) An extremely small (or zero or negative) parallax is interpreted
86** to mean that the object is on the "celestial sphere", the radius
87** of which is an arbitrary (large) value (see the constant PXMIN).
88** When the distance is overridden in this way, the status,
89** initially zero, has 1 added to it.
90**
91** 7) If the space velocity is a significant fraction of c (see the
92** constant VMAX), it is arbitrarily set to zero. When this action
93** occurs, 2 is added to the status.
94**
95** 8) The relativistic adjustment involves an iterative calculation.
96** If the process fails to converge within a set number (IMAX) of
97** iterations, 4 is added to the status.
98**
99** 9) The inverse transformation is performed by the function
100** eraPvstar.
101**
102** Called:
103** eraS2pv spherical coordinates to pv-vector
104** eraPm modulus of p-vector
105** eraZp zero p-vector
106** eraPn decompose p-vector into modulus and direction
107** eraPdp scalar product of two p-vectors
108** eraSxp multiply p-vector by scalar
109** eraPmp p-vector minus p-vector
110** eraPpp p-vector plus p-vector
111**
112** Reference:
113**
114** Stumpff, P., 1985, Astron.Astrophys. 144, 232-240.
115**
116** Copyright (C) 2013-2017, NumFOCUS Foundation.
117** Derived, with permission, from the SOFA library. See notes at end of file.
118*/
119{
120/* Smallest allowed parallax */
121 static const double PXMIN = 1e-7;
122
123/* Largest allowed speed (fraction of c) */
124 static const double VMAX = 0.5;
125
126/* Maximum number of iterations for relativistic solution */
127 static const int IMAX = 100;
128
129 int i, iwarn;
130 double w, r, rd, rad, decd, v, x[3], usr[3], ust[3],
131 vsr, vst, betst, betsr, bett, betr,
132 dd, ddel, ur[3], ut[3],
133 d = 0.0, del = 0.0, /* to prevent */
134 odd = 0.0, oddel = 0.0, /* compiler */
135 od = 0.0, odel = 0.0; /* warnings */
136
137
138/* Distance (au). */
139 if (px >= PXMIN) {
140 w = px;
141 iwarn = 0;
142 } else {
143 w = PXMIN;
144 iwarn = 1;
145 }
146 r = ERFA_DR2AS / w;
147
148/* Radial velocity (au/day). */
149 rd = ERFA_DAYSEC * rv * 1e3 / ERFA_DAU;
150
151/* Proper motion (radian/day). */
152 rad = pmr / ERFA_DJY;
153 decd = pmd / ERFA_DJY;
154
155/* To pv-vector (au,au/day). */
156 eraS2pv(ra, dec, r, rad, decd, rd, pv);
157
158/* If excessive velocity, arbitrarily set it to zero. */
159 v = eraPm(pv[1]);
160 if (v / ERFA_DC > VMAX) {
161 eraZp(pv[1]);
162 iwarn += 2;
163 }
164
165/* Isolate the radial component of the velocity (au/day). */
166 eraPn(pv[0], &w, x);
167 vsr = eraPdp(x, pv[1]);
168 eraSxp(vsr, x, usr);
169
170/* Isolate the transverse component of the velocity (au/day). */
171 eraPmp(pv[1], usr, ust);
172 vst = eraPm(ust);
173
174/* Special-relativity dimensionless parameters. */
175 betsr = vsr / ERFA_DC;
176 betst = vst / ERFA_DC;
177
178/* Determine the inertial-to-observed relativistic correction terms. */
179 bett = betst;
180 betr = betsr;
181 for (i = 0; i < IMAX; i++) {
182 d = 1.0 + betr;
183 w = betr*betr + bett*bett;
184 del = - w / (sqrt(1.0 - w) + 1.0);
185 betr = d * betsr + del;
186 bett = d * betst;
187 if (i > 0) {
188 dd = fabs(d - od);
189 ddel = fabs(del - odel);
190 if ((i > 1) && (dd >= odd) && (ddel >= oddel)) break;
191 odd = dd;
192 oddel = ddel;
193 }
194 od = d;
195 odel = del;
196 }
197 if (i >= IMAX) iwarn += 4;
198
199/* Replace observed radial velocity with inertial value. */
200 w = (betsr != 0.0) ? d + del / betsr : 1.0;
201 eraSxp(w, usr, ur);
202
203/* Replace observed tangential velocity with inertial value. */
204 eraSxp(d, ust, ut);
205
206/* Combine the two to obtain the inertial space velocity. */
207 eraPpp(ur, ut, pv[1]);
208
209/* Return the status. */
210 return iwarn;
211
212}
213/*----------------------------------------------------------------------
214**
215**
216** Copyright (C) 2013-2017, NumFOCUS Foundation.
217** All rights reserved.
218**
219** This library is derived, with permission, from the International
220** Astronomical Union's "Standards of Fundamental Astronomy" library,
221** available from http://www.iausofa.org.
222**
223** The ERFA version is intended to retain identical functionality to
224** the SOFA library, but made distinct through different function and
225** file names, as set out in the SOFA license conditions. The SOFA
226** original has a role as a reference standard for the IAU and IERS,
227** and consequently redistribution is permitted only in its unaltered
228** state. The ERFA version is not subject to this restriction and
229** therefore can be included in distributions which do not support the
230** concept of "read only" software.
231**
232** Although the intent is to replicate the SOFA API (other than
233** replacement of prefix names) and results (with the exception of
234** bugs; any that are discovered will be fixed), SOFA is not
235** responsible for any errors found in this version of the library.
236**
237** If you wish to acknowledge the SOFA heritage, please acknowledge
238** that you are using a library derived from SOFA, rather than SOFA
239** itself.
240**
241**
242** TERMS AND CONDITIONS
243**
244** Redistribution and use in source and binary forms, with or without
245** modification, are permitted provided that the following conditions
246** are met:
247**
248** 1 Redistributions of source code must retain the above copyright
249** notice, this list of conditions and the following disclaimer.
250**
251** 2 Redistributions in binary form must reproduce the above copyright
252** notice, this list of conditions and the following disclaimer in
253** the documentation and/or other materials provided with the
254** distribution.
255**
256** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
257** the International Astronomical Union nor the names of its
258** contributors may be used to endorse or promote products derived
259** from this software without specific prior written permission.
260**
261** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
262** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
263** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
264** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
265** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
266** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
267** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
268** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
269** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
270** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
271** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
272** POSSIBILITY OF SUCH DAMAGE.
273**
274*/
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