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
|
/*
*+
* Name:
* palDh2e
* Purpose:
* Horizon to equatorial coordinates: Az,El to HA,Dec
* Language:
* Starlink ANSI C
* Type of Module:
* Library routine
* Invocation:
* palDh2e( double az, double el, double phi, double * ha, double * dec );
* Arguments:
* az = double (Given)
* Azimuth (radians)
* el = double (Given)
* Elevation (radians)
* phi = double (Given)
* Observatory latitude (radians)
* ha = double * (Returned)
* Hour angle (radians)
* dec = double * (Returned)
* Declination (radians)
* Description:
* Convert horizon to equatorial coordinates.
* Authors:
* PTW: Pat Wallace (STFC)
* TIMJ: Tim Jenness (JAC, Hawaii)
* {enter_new_authors_here}
* Notes:
* - All the arguments are angles in radians.
* - The sign convention for azimuth is north zero, east +pi/2.
* - HA is returned in the range +/-pi. Declination is returned
* in the range +/-pi/2.
* - The latitude is (in principle) geodetic. In critical
* applications, corrections for polar motion should be applied.
* - In some applications it will be important to specify the
* correct type of elevation in order to produce the required
* type of HA,Dec. In particular, it may be important to
* distinguish between the elevation as affected by refraction,
* which will yield the "observed" HA,Dec, and the elevation
* in vacuo, which will yield the "topocentric" HA,Dec. If the
* effects of diurnal aberration can be neglected, the
* topocentric HA,Dec may be used as an approximation to the
* "apparent" HA,Dec.
* - No range checking of arguments is done.
* - In applications which involve many such calculations, rather
* than calling the present routine it will be more efficient to
* use inline code, having previously computed fixed terms such
* as sine and cosine of latitude.
* History:
* 2012-02-08 (TIMJ):
* Initial version with documentation taken from Fortran SLA
* Adapted with permission from the Fortran SLALIB library.
* {enter_further_changes_here}
* Copyright:
* Copyright (C) 1996 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 Lesser 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General
* License along with this program. If not, see
* <http://www.gnu.org/licenses/>.
* Bugs:
* {note_any_bugs_here}
*-
*/
#include "pal.h"
#include <math.h>
void
palDh2e ( double az, double el, double phi, double *ha, double *dec) {
double sa;
double ca;
double se;
double ce;
double sp;
double cp;
double x;
double y;
double z;
double r;
/* Useful trig functions */
sa = sin(az);
ca = cos(az);
se = sin(el);
ce = cos(el);
sp = sin(phi);
cp = cos(phi);
/* HA,Dec as x,y,z */
x = -ca * ce * sp + se * cp;
y = -sa * ce;
z = ca * ce * cp + se * sp;
/* To HA,Dec */
r = sqrt(x * x + y * y);
if (r == 0.) {
*ha = 0.;
} else {
*ha = atan2(y, x);
}
*dec = atan2(z, r);
return;
}
|
