1 /*
2 *+
3 * Name:
4 * palOap
5
6 * Purpose:
7 * Observed to apparent place
8
9 * Language:
10 * Starlink ANSI C
11
12 * Type of Module:
13 * Library routine
14
15 * Invocation:
16 * void palOap ( const char *type, double ob1, double ob2, double date,
17 * double dut, double elongm, double phim, double hm,
18 * double xp, double yp, double tdk, double pmb,
19 * double rh, double wl, double tlr,
20 * double *rap, double *dap );
21
22 * Arguments:
23 * type = const char * (Given)
24 * Type of coordinates - 'R', 'H' or 'A' (see below)
25 * ob1 = double (Given)
26 * Observed Az, HA or RA (radians; Az is N=0;E=90)
27 * ob2 = double (Given)
28 * Observed ZD or Dec (radians)
29 * date = double (Given)
30 * UTC date/time (Modified Julian Date, JD-2400000.5)
31 * dut = double (Given)
32 * delta UT: UT1-UTC (UTC seconds)
33 * elongm = double (Given)
34 * Mean longitude of the observer (radians, east +ve)
35 * phim = double (Given)
36 * Mean geodetic latitude of the observer (radians)
37 * hm = double (Given)
38 * Observer's height above sea level (metres)
39 * xp = double (Given)
40 * Polar motion x-coordinates (radians)
41 * yp = double (Given)
42 * Polar motion y-coordinates (radians)
43 * tdk = double (Given)
44 * Local ambient temperature (K; std=273.15)
45 * pmb = double (Given)
46 * Local atmospheric pressure (mb; std=1013.25)
47 * rh = double (Given)
48 * Local relative humidity (in the range 0.0-1.0)
49 * wl = double (Given)
50 * Effective wavelength (micron, e.g. 0.55)
51 * tlr = double (Given)
52 * Tropospheric laps rate (K/metre, e.g. 0.0065)
53 * rap = double * (Given)
54 * Geocentric apparent right ascension
55 * dap = double * (Given)
56 * Geocentric apparent declination
57
58 * Description:
59 * Observed to apparent place.
60
61 * Authors:
62 * PTW: Patrick T. Wallace
63 * TIMJ: Tim Jenness (JAC, Hawaii)
64 * {enter_new_authors_here}
65
66 * Notes:
67 * - Only the first character of the TYPE argument is significant.
68 * 'R' or 'r' indicates that OBS1 and OBS2 are the observed right
69 * ascension and declination; 'H' or 'h' indicates that they are
70 * hour angle (west +ve) and declination; anything else ('A' or
71 * 'a' is recommended) indicates that OBS1 and OBS2 are azimuth
72 * (north zero, east 90 deg) and zenith distance. (Zenith
73 * distance is used rather than elevation in order to reflect the
74 * fact that no allowance is made for depression of the horizon.)
75 *
76 * - The accuracy of the result is limited by the corrections for
77 * refraction. Providing the meteorological parameters are
78 * known accurately and there are no gross local effects, the
79 * predicted apparent RA,Dec should be within about 0.1 arcsec
80 * for a zenith distance of less than 70 degrees. Even at a
81 * topocentric zenith distance of 90 degrees, the accuracy in
82 * elevation should be better than 1 arcmin; useful results
83 * are available for a further 3 degrees, beyond which the
84 * palRefro routine returns a fixed value of the refraction.
85 * The complementary routines palAop (or palAopqk) and palOap
86 * (or palOapqk) are self-consistent to better than 1 micro-
87 * arcsecond all over the celestial sphere.
88 *
89 * - It is advisable to take great care with units, as even
90 * unlikely values of the input parameters are accepted and
91 * processed in accordance with the models used.
92 *
93 * - "Observed" Az,El means the position that would be seen by a
94 * perfect theodolite located at the observer. This is
95 * related to the observed HA,Dec via the standard rotation, using
96 * the geodetic latitude (corrected for polar motion), while the
97 * observed HA and RA are related simply through the local
98 * apparent ST. "Observed" RA,Dec or HA,Dec thus means the
99 * position that would be seen by a perfect equatorial located
100 * at the observer and with its polar axis aligned to the
101 * Earth's axis of rotation (n.b. not to the refracted pole).
102 * By removing from the observed place the effects of
103 * atmospheric refraction and diurnal aberration, the
104 * geocentric apparent RA,Dec is obtained.
105 *
106 * - Frequently, mean rather than apparent RA,Dec will be required,
107 * in which case further transformations will be necessary. The
108 * palAmp etc routines will convert the apparent RA,Dec produced
109 * by the present routine into an "FK5" (J2000) mean place, by
110 * allowing for the Sun's gravitational lens effect, annual
111 * aberration, nutation and precession. Should "FK4" (1950)
112 * coordinates be needed, the routines palFk524 etc will also
113 * need to be applied.
114 *
115 * - To convert to apparent RA,Dec the coordinates read from a
116 * real telescope, corrections would have to be applied for
117 * encoder zero points, gear and encoder errors, tube flexure,
118 * the position of the rotator axis and the pointing axis
119 * relative to it, non-perpendicularity between the mounting
120 * axes, and finally for the tilt of the azimuth or polar axis
121 * of the mounting (with appropriate corrections for mount
122 * flexures). Some telescopes would, of course, exhibit other
123 * properties which would need to be accounted for at the
124 * appropriate point in the sequence.
125 *
126 * - This routine takes time to execute, due mainly to the rigorous
127 * integration used to evaluate the refraction. For processing
128 * multiple stars for one location and time, call palAoppa once
129 * followed by one call per star to palOapqk. Where a range of
130 * times within a limited period of a few hours is involved, and the
131 * highest precision is not required, call palAoppa once, followed
132 * by a call to palAoppat each time the time changes, followed by
133 * one call per star to palOapqk.
134 *
135 * - The DATE argument is UTC expressed as an MJD. This is, strictly
136 * speaking, wrong, because of leap seconds. However, as long as
137 * the delta UT and the UTC are consistent there are no
138 * difficulties, except during a leap second. In this case, the
139 * start of the 61st second of the final minute should begin a new
140 * MJD day and the old pre-leap delta UT should continue to be used.
141 * As the 61st second completes, the MJD should revert to the start
142 * of the day as, simultaneously, the delta UTC changes by one
143 * second to its post-leap new value.
144 *
145 * - The delta UT (UT1-UTC) is tabulated in IERS circulars and
146 * elsewhere. It increases by exactly one second at the end of
147 * each UTC leap second, introduced in order to keep delta UT
148 * within +/- 0.9 seconds.
149 *
150 * - IMPORTANT -- TAKE CARE WITH THE LONGITUDE SIGN CONVENTION.
151 * The longitude required by the present routine is east-positive,
152 * in accordance with geographical convention (and right-handed).
153 * In particular, note that the longitudes returned by the
154 * palOBS routine are west-positive, following astronomical
155 * usage, and must be reversed in sign before use in the present
156 * routine.
157 *
158 * - The polar coordinates XP,YP can be obtained from IERS
159 * circulars and equivalent publications. The maximum amplitude
160 * is about 0.3 arcseconds. If XP,YP values are unavailable,
161 * use XP=YP=0D0. See page B60 of the 1988 Astronomical Almanac
162 * for a definition of the two angles.
163 *
164 * - The height above sea level of the observing station, HM,
165 * can be obtained from the Astronomical Almanac (Section J
166 * in the 1988 edition), or via the routine palOBS. If P,
167 * the pressure in millibars, is available, an adequate
168 * estimate of HM can be obtained from the expression
169 *
170 * HM ~ -29.3*TSL*LOG(P/1013.25).
171 *
172 * where TSL is the approximate sea-level air temperature in K
173 * (see Astrophysical Quantities, C.W.Allen, 3rd edition,
174 * section 52). Similarly, if the pressure P is not known,
175 * it can be estimated from the height of the observing
176 * station, HM, as follows:
177 *
178 * P ~ 1013.25*EXP(-HM/(29.3*TSL)).
179 *
180 * Note, however, that the refraction is nearly proportional to the
181 * pressure and that an accurate P value is important for precise
182 * work.
183 *
184 * - The azimuths etc. used by the present routine are with respect
185 * to the celestial pole. Corrections from the terrestrial pole
186 * can be computed using palPolmo.
187
188 * History:
189 * 2012-08-27 (TIMJ):
190 * Initial version, copied from Fortran SLA
191 * Adapted with permission from the Fortran SLALIB library.
192 * {enter_further_changes_here}
193
194 * Copyright:
195 * Copyright (C) 2005 Patrick T. Wallace
196 * Copyright (C) 2012 Science and Technology Facilities Council.
197 * All Rights Reserved.
198
199 * Licence:
200 * This program is free software; you can redistribute it and/or
201 * modify it under the terms of the GNU General Public License as
202 * published by the Free Software Foundation; either version 3 of
203 * the License, or (at your option) any later version.
204 *
205 * This program is distributed in the hope that it will be
206 * useful, but WITHOUT ANY WARRANTY; without even the implied
207 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
208 * PURPOSE. See the GNU General Public License for more details.
209 *
210 * You should have received a copy of the GNU General Public License
211 * along with this program; if not, write to the Free Software
212 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
213 * MA 02110-1301, USA.
214
215 * Bugs:
216 * {note_any_bugs_here}
217 *-
218 */
219
220 #include "pal.h"
221
palOap(const char * type,double ob1,double ob2,double date,double dut,double elongm,double phim,double hm,double xp,double yp,double tdk,double pmb,double rh,double wl,double tlr,double * rap,double * dap)222 void palOap ( const char *type, double ob1, double ob2, double date,
223 double dut, double elongm, double phim, double hm,
224 double xp, double yp, double tdk, double pmb,
225 double rh, double wl, double tlr,
226 double *rap, double *dap ) {
227
228 double aoprms[14];
229
230 palAoppa(date,dut,elongm,phim,hm,xp,yp,tdk,pmb,rh,wl,tlr,
231 aoprms);
232 palOapqk(type,ob1,ob2,aoprms,rap,dap);
233
234 }
235