File: palAopqk.c

package info (click to toggle)
starlink-pal 0.9.8-1
  • links: PTS, VCS
  • area: main
  • in suites: bullseye, buster, sid
  • size: 1,808 kB
  • sloc: ansic: 6,689; makefile: 128; sh: 81
file content (288 lines) | stat: -rw-r--r-- 10,270 bytes parent folder | download
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
/*
*+
*  Name:
*     palAopqk

*  Purpose:
*     Quick apparent to observed place

*  Language:
*     Starlink ANSI C

*  Type of Module:
*     Library routine

*  Invocation:
*     void palAopqk ( double rap, double dap, const double aoprms[14],
*                     double *aob, double *zob, double *hob,
*                     double *dob, double *rob );

*  Arguments:
*     rap = double (Given)
*        Geocentric apparent right ascension
*     dap = double (Given)
*        Geocentric apparent declination
*     aoprms = const double [14] (Given)
*        Star-independent apparent-to-observed parameters.
*
*         [0]      geodetic latitude (radians)
*         [1,2]    sine and cosine of geodetic latitude
*         [3]      magnitude of diurnal aberration vector
*         [4]      height (HM)
*         [5]      ambient temperature (T)
*         [6]      pressure (P)
*         [7]      relative humidity (RH)
*         [8]      wavelength (WL)
*         [9]      lapse rate (TLR)
*         [10,11]  refraction constants A and B (radians)
*         [12]     longitude + eqn of equinoxes + sidereal DUT (radians)
*         [13]     local apparent sidereal time (radians)
*     aob = double * (Returned)
*        Observed azimuth (radians: N=0,E=90)
*     zob = double * (Returned)
*        Observed zenith distance (radians)
*     hob = double * (Returned)
*        Observed Hour Angle (radians)
*     dob = double * (Returned)
*        Observed Declination (radians)
*     rob = double * (Returned)
*        Observed Right Ascension (radians)

*  Description:
*     Quick apparent to observed place.

*  Authors:
*     TIMJ: Tim Jenness (JAC, Hawaii)
*     PTW: Patrick T. Wallace
*     {enter_new_authors_here}

*  Notes:
*     - This routine returns zenith distance rather than elevation
*       in order to reflect the fact that no allowance is made for
*       depression of the horizon.
*
*     - The accuracy of the result is limited by the corrections for
*       refraction.  Providing the meteorological parameters are
*       known accurately and there are no gross local effects, the
*       observed RA,Dec predicted by this routine should be within
*       about 0.1 arcsec for a zenith distance of less than 70 degrees.
*       Even at a topocentric zenith distance of 90 degrees, the
*       accuracy in elevation should be better than 1 arcmin;  useful
*       results are available for a further 3 degrees, beyond which
*       the palRefro routine returns a fixed value of the refraction.
*       The complementary routines palAop (or palAopqk) and palOap
*       (or palOapqk) are self-consistent to better than 1 micro-
*       arcsecond all over the celestial sphere.
*
*     - It is advisable to take great care with units, as even
*       unlikely values of the input parameters are accepted and
*       processed in accordance with the models used.
*
*     - "Apparent" place means the geocentric apparent right ascension
*       and declination, which is obtained from a catalogue mean place
*       by allowing for space motion, parallax, precession, nutation,
*       annual aberration, and the Sun's gravitational lens effect.  For
*       star positions in the FK5 system (i.e. J2000), these effects can
*       be applied by means of the palMap etc routines.  Starting from
*       other mean place systems, additional transformations will be
*       needed;  for example, FK4 (i.e. B1950) mean places would first
*       have to be converted to FK5, which can be done with the
*       palFk425 etc routines.
*
*     - "Observed" Az,El means the position that would be seen by a
*       perfect theodolite located at the observer.  This is obtained
*       from the geocentric apparent RA,Dec by allowing for Earth
*       orientation and diurnal aberration, rotating from equator
*       to horizon coordinates, and then adjusting for refraction.
*       The HA,Dec is obtained by rotating back into equatorial
*       coordinates, using the geodetic latitude corrected for polar
*       motion, and is the position that would be seen by a perfect
*       equatorial located at the observer and with its polar axis
*       aligned to the Earth's axis of rotation (n.b. not to the
*       refracted pole).  Finally, the RA is obtained by subtracting
*       the HA from the local apparent ST.
*
*     - To predict the required setting of a real telescope, the
*       observed place produced by this routine would have to be
*       adjusted for the tilt of the azimuth or polar axis of the
*       mounting (with appropriate corrections for mount flexures),
*       for non-perpendicularity between the mounting axes, for the
*       position of the rotator axis and the pointing axis relative
*       to it, for tube flexure, for gear and encoder errors, and
*       finally for encoder zero points.  Some telescopes would, of
*       course, exhibit other properties which would need to be
*       accounted for at the appropriate point in the sequence.
*
*     - The star-independent apparent-to-observed-place parameters
*       in AOPRMS may be computed by means of the palAoppa routine.
*       If nothing has changed significantly except the time, the
*       palAoppat routine may be used to perform the requisite
*       partial recomputation of AOPRMS.
*
*     - At zenith distances beyond about 76 degrees, the need for
*       special care with the corrections for refraction causes a
*       marked increase in execution time.  Moreover, the effect
*       gets worse with increasing zenith distance.  Adroit
*       programming in the calling application may allow the
*       problem to be reduced.  Prepare an alternative AOPRMS array,
*       computed for zero air-pressure;  this will disable the
*       refraction corrections and cause rapid execution.  Using
*       this AOPRMS array, a preliminary call to the present routine
*       will, depending on the application, produce a rough position
*       which may be enough to establish whether the full, slow
*       calculation (using the real AOPRMS array) is worthwhile.
*       For example, there would be no need for the full calculation
*       if the preliminary call had already established that the
*       source was well below the elevation limits for a particular
*       telescope.
*
*     - The azimuths etc produced by the present routine are with
*       respect to the celestial pole.  Corrections to the terrestrial
*       pole can be computed using palPolmo.

*  History:
*     2012-08-25 (TIMJ):
*        Initial version, copied from Fortran SLA
*        Adapted with permission from the Fortran SLALIB library.
*     {enter_further_changes_here}

*  Copyright:
*     Copyright (C) 2003 Rutherford Appleton Laboratory
*     Copyright (C) 2012 Science and Technology Facilities Council.
*     All Rights Reserved.

*  Licence:
*     This program is free software; you can redistribute it and/or
*     modify it under the terms of the GNU General Public License as
*     published by the Free Software Foundation; either version 3 of
*     the License, or (at your option) any later version.
*
*     This program is distributed in the hope that it will be
*     useful, but WITHOUT ANY WARRANTY; without even the implied
*     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
*     PURPOSE. See the GNU General Public License for more details.
*
*     You should have received a copy of the GNU General Public License
*     along with this program; if not, write to the Free Software
*     Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
*     MA 02110-1301, USA.

*  Bugs:
*     {note_any_bugs_here}
*-
*/

#include <math.h>

#include "pal.h"

void palAopqk ( double rap, double dap, const double aoprms[14],
                double *aob, double *zob, double *hob,
                double *dob, double *rob ) {

  /*  Breakpoint for fast/slow refraction algorithm:
   *  ZD greater than arctan(4), (see palRefco routine)
   *  or vector Z less than cosine(arctan(Z)) = 1/sqrt(17) */
  const double zbreak = 0.242535625;
  int i;

  double  sphi,cphi,st,v[3],xhd,yhd,zhd,diurab,f,
    xhdt,yhdt,zhdt,xaet,yaet,zaet,azobs,
    zdt,refa,refb,zdobs,dzd,dref,ce,
    xaeo,yaeo,zaeo,hmobs,dcobs,raobs;

  /*  sin, cos of latitude */
  sphi = aoprms[1];
  cphi = aoprms[2];

  /*  local apparent sidereal time */
  st = aoprms[13];

  /*  apparent ra,dec to cartesian -ha,dec */
  palDcs2c( rap-st, dap, v );
  xhd = v[0];
  yhd = v[1];
  zhd = v[2];

  /*  diurnal aberration */
  diurab = aoprms[3];
  f = (1.0-diurab*yhd);
  xhdt = f*xhd;
  yhdt = f*(yhd+diurab);
  zhdt = f*zhd;

  /*  cartesian -ha,dec to cartesian az,el (s=0,e=90) */
  xaet = sphi*xhdt-cphi*zhdt;
  yaet = yhdt;
  zaet = cphi*xhdt+sphi*zhdt;

  /*  azimuth (n=0,e=90) */
  if (xaet == 0.0 && yaet == 0.0) {
    azobs = 0.0;
  } else {
    azobs = atan2(yaet,-xaet);
  }

  /*  topocentric zenith distance */
  zdt = atan2(sqrt(xaet*xaet+yaet*yaet),zaet);

  /*
   *  refraction
   *  ---------- */

  /*  fast algorithm using two constant model */
  refa = aoprms[10];
  refb = aoprms[11];
  palRefz(zdt,refa,refb,&zdobs);

  /*  large zenith distance? */
  if (cos(zdobs) < zbreak) {

    /*     yes: use rigorous algorithm */

    /*     initialize loop (maximum of 10 iterations) */
    i = 1;
    dzd = 1.0e1;
    while (fabs(dzd) > 1e-10 && i <= 10) {

      /*        compute refraction using current estimate of observed zd */
      palRefro(zdobs,aoprms[4],aoprms[5],aoprms[6],
               aoprms[7],aoprms[8],aoprms[0],
               aoprms[9],1e-8,&dref);

      /*        remaining discrepancy */
      dzd = zdobs+dref-zdt;

      /*        update the estimate */
      zdobs = zdobs-dzd;

      /*        increment the iteration counter */
      i++;
    }
  }

  /*  to cartesian az/zd */
  ce = sin(zdobs);
  xaeo = -cos(azobs)*ce;
  yaeo = sin(azobs)*ce;
  zaeo = cos(zdobs);

  /*  cartesian az/zd to cartesian -ha,dec */
  v[0] = sphi*xaeo+cphi*zaeo;
  v[1] = yaeo;
  v[2] = -cphi*xaeo+sphi*zaeo;

  /*  to spherical -ha,dec */
  palDcc2s(v,&hmobs,&dcobs);

  /*  right ascension */
  raobs = palDranrm(st+hmobs);

  /*  return the results */
  *aob = azobs;
  *zob = zdobs;
  *hob = -hmobs;
  *dob = dcobs;
  *rob = raobs;

}