source: trunk/FACT++/erfa/src/atoiq.c

Last change on this file was 18921, checked in by tbretz, 7 years ago
Updated to ERFA 1.4.0
File size: 9.6 KB
Line 
1#include "erfa.h"
2
3void eraAtoiq(const char *type,
4 double ob1, double ob2, eraASTROM *astrom,
5 double *ri, double *di)
6/*
7** - - - - - - - - -
8** e r a A t o i q
9** - - - - - - - - -
10**
11** Quick observed place to CIRS, given the star-independent astrometry
12** parameters.
13**
14** Use of this function is appropriate when efficiency is important and
15** where many star positions are all to be transformed for one date.
16** The star-independent astrometry parameters can be obtained by
17** calling eraApio[13] or eraApco[13].
18**
19** Given:
20** type char[] type of coordinates: "R", "H" or "A" (Note 1)
21** ob1 double observed Az, HA or RA (radians; Az is N=0,E=90)
22** ob2 double observed ZD or Dec (radians)
23** astrom eraASTROM* star-independent astrometry parameters:
24** pmt double PM time interval (SSB, Julian years)
25** eb double[3] SSB to observer (vector, au)
26** eh double[3] Sun to observer (unit vector)
27** em double distance from Sun to observer (au)
28** v double[3] barycentric observer velocity (vector, c)
29** bm1 double sqrt(1-|v|^2): reciprocal of Lorenz factor
30** bpn double[3][3] bias-precession-nutation matrix
31** along double longitude + s' (radians)
32** xpl double polar motion xp wrt local meridian (radians)
33** ypl double polar motion yp wrt local meridian (radians)
34** sphi double sine of geodetic latitude
35** cphi double cosine of geodetic latitude
36** diurab double magnitude of diurnal aberration vector
37** eral double "local" Earth rotation angle (radians)
38** refa double refraction constant A (radians)
39** refb double refraction constant B (radians)
40**
41** Returned:
42** ri double* CIRS right ascension (CIO-based, radians)
43** di double* CIRS declination (radians)
44**
45** Notes:
46**
47** 1) "Observed" Az,El means the position that would be seen by a
48** perfect geodetically aligned theodolite. This is related to
49** the observed HA,Dec via the standard rotation, using the geodetic
50** latitude (corrected for polar motion), while the observed HA and
51** RA are related simply through the Earth rotation angle and the
52** site longitude. "Observed" RA,Dec or HA,Dec thus means the
53** position that would be seen by a perfect equatorial with its
54** polar axis aligned to the Earth's axis of rotation. By removing
55** from the observed place the effects of atmospheric refraction and
56** diurnal aberration, the CIRS RA,Dec is obtained.
57**
58** 2) Only the first character of the type argument is significant.
59** "R" or "r" indicates that ob1 and ob2 are the observed right
60** ascension and declination; "H" or "h" indicates that they are
61** hour angle (west +ve) and declination; anything else ("A" or
62** "a" is recommended) indicates that ob1 and ob2 are azimuth (north
63** zero, east 90 deg) and zenith distance. (Zenith distance is used
64** rather than altitude in order to reflect the fact that no
65** allowance is made for depression of the horizon.)
66**
67** 3) The accuracy of the result is limited by the corrections for
68** refraction, which use a simple A*tan(z) + B*tan^3(z) model.
69** Providing the meteorological parameters are known accurately and
70** there are no gross local effects, the predicted observed
71** coordinates should be within 0.05 arcsec (optical) or 1 arcsec
72** (radio) for a zenith distance of less than 70 degrees, better
73** than 30 arcsec (optical or radio) at 85 degrees and better than
74** 20 arcmin (optical) or 30 arcmin (radio) at the horizon.
75**
76** Without refraction, the complementary functions eraAtioq and
77** eraAtoiq are self-consistent to better than 1 microarcsecond all
78** over the celestial sphere. With refraction included, consistency
79** falls off at high zenith distances, but is still better than
80** 0.05 arcsec at 85 degrees.
81**
82** 4) It is advisable to take great care with units, as even unlikely
83** values of the input parameters are accepted and processed in
84** accordance with the models used.
85**
86** Called:
87** eraS2c spherical coordinates to unit vector
88** eraC2s p-vector to spherical
89** eraAnp normalize angle into range 0 to 2pi
90**
91** Copyright (C) 2013-2017, NumFOCUS Foundation.
92** Derived, with permission, from the SOFA library. See notes at end of file.
93*/
94{
95 int c;
96 double c1, c2, sphi, cphi, ce, xaeo, yaeo, zaeo, v[3],
97 xmhdo, ymhdo, zmhdo, az, sz, zdo, refa, refb, tz, dref,
98 zdt, xaet, yaet, zaet, xmhda, ymhda, zmhda,
99 f, xhd, yhd, zhd, xpl, ypl, w, hma;
100
101
102/* Coordinate type. */
103 c = (int) type[0];
104
105/* Coordinates. */
106 c1 = ob1;
107 c2 = ob2;
108
109/* Sin, cos of latitude. */
110 sphi = astrom->sphi;
111 cphi = astrom->cphi;
112
113/* Standardize coordinate type. */
114 if ( c == 'r' || c == 'R' ) {
115 c = 'R';
116 } else if ( c == 'h' || c == 'H' ) {
117 c = 'H';
118 } else {
119 c = 'A';
120 }
121
122/* If Az,ZD, convert to Cartesian (S=0,E=90). */
123 if ( c == 'A' ) {
124 ce = sin(c2);
125 xaeo = - cos(c1) * ce;
126 yaeo = sin(c1) * ce;
127 zaeo = cos(c2);
128
129 } else {
130
131 /* If RA,Dec, convert to HA,Dec. */
132 if ( c == 'R' ) c1 = astrom->eral - c1;
133
134 /* To Cartesian -HA,Dec. */
135 eraS2c ( -c1, c2, v );
136 xmhdo = v[0];
137 ymhdo = v[1];
138 zmhdo = v[2];
139
140 /* To Cartesian Az,El (S=0,E=90). */
141 xaeo = sphi*xmhdo - cphi*zmhdo;
142 yaeo = ymhdo;
143 zaeo = cphi*xmhdo + sphi*zmhdo;
144 }
145
146/* Azimuth (S=0,E=90). */
147 az = ( xaeo != 0.0 || yaeo != 0.0 ) ? atan2(yaeo,xaeo) : 0.0;
148
149/* Sine of observed ZD, and observed ZD. */
150 sz = sqrt ( xaeo*xaeo + yaeo*yaeo );
151 zdo = atan2 ( sz, zaeo );
152
153/*
154** Refraction
155** ----------
156*/
157
158/* Fast algorithm using two constant model. */
159 refa = astrom->refa;
160 refb = astrom->refb;
161 tz = sz / zaeo;
162 dref = ( refa + refb*tz*tz ) * tz;
163 zdt = zdo + dref;
164
165/* To Cartesian Az,ZD. */
166 ce = sin(zdt);
167 xaet = cos(az) * ce;
168 yaet = sin(az) * ce;
169 zaet = cos(zdt);
170
171/* Cartesian Az,ZD to Cartesian -HA,Dec. */
172 xmhda = sphi*xaet + cphi*zaet;
173 ymhda = yaet;
174 zmhda = - cphi*xaet + sphi*zaet;
175
176/* Diurnal aberration. */
177 f = ( 1.0 + astrom->diurab*ymhda );
178 xhd = f * xmhda;
179 yhd = f * ( ymhda - astrom->diurab );
180 zhd = f * zmhda;
181
182/* Polar motion. */
183 xpl = astrom->xpl;
184 ypl = astrom->ypl;
185 w = xpl*xhd - ypl*yhd + zhd;
186 v[0] = xhd - xpl*w;
187 v[1] = yhd + ypl*w;
188 v[2] = w - ( xpl*xpl + ypl*ypl ) * zhd;
189
190/* To spherical -HA,Dec. */
191 eraC2s(v, &hma, di);
192
193/* Right ascension. */
194 *ri = eraAnp(astrom->eral + hma);
195
196/* Finished. */
197
198}
199/*----------------------------------------------------------------------
200**
201**
202** Copyright (C) 2013-2017, NumFOCUS Foundation.
203** All rights reserved.
204**
205** This library is derived, with permission, from the International
206** Astronomical Union's "Standards of Fundamental Astronomy" library,
207** available from http://www.iausofa.org.
208**
209** The ERFA version is intended to retain identical functionality to
210** the SOFA library, but made distinct through different function and
211** file names, as set out in the SOFA license conditions. The SOFA
212** original has a role as a reference standard for the IAU and IERS,
213** and consequently redistribution is permitted only in its unaltered
214** state. The ERFA version is not subject to this restriction and
215** therefore can be included in distributions which do not support the
216** concept of "read only" software.
217**
218** Although the intent is to replicate the SOFA API (other than
219** replacement of prefix names) and results (with the exception of
220** bugs; any that are discovered will be fixed), SOFA is not
221** responsible for any errors found in this version of the library.
222**
223** If you wish to acknowledge the SOFA heritage, please acknowledge
224** that you are using a library derived from SOFA, rather than SOFA
225** itself.
226**
227**
228** TERMS AND CONDITIONS
229**
230** Redistribution and use in source and binary forms, with or without
231** modification, are permitted provided that the following conditions
232** are met:
233**
234** 1 Redistributions of source code must retain the above copyright
235** notice, this list of conditions and the following disclaimer.
236**
237** 2 Redistributions in binary form must reproduce the above copyright
238** notice, this list of conditions and the following disclaimer in
239** the documentation and/or other materials provided with the
240** distribution.
241**
242** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
243** the International Astronomical Union nor the names of its
244** contributors may be used to endorse or promote products derived
245** from this software without specific prior written permission.
246**
247** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
248** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
249** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
250** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
251** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
252** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
253** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
254** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
255** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
256** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
257** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
258** POSSIBILITY OF SUCH DAMAGE.
259**
260*/
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