File Coverage

palsrc/palDs2tp.c

Criterion	Covered	Total	%
statement	0	19	0.0
branch	0	6	0.0
condition			n/a
subroutine			n/a
pod			n/a
total	0	25	0.0

line	stmt	bran	code
1			/*
2			*+
3			* Name:
4			* palDs2tp
5
6			* Purpose:
7			* Spherical to tangent plane projection
8
9			* Language:
10			* Starlink ANSI C
11
12			* Type of Module:
13			* Library routine
14
15			* Invocation:
16			* palDs2tp( double ra, double dec, double raz, double decz,
17			* double xi, double eta, int *j );
18
19			* Arguments:
20			* ra = double (Given)
21			* RA spherical coordinate of point to be projected (radians)
22			* dec = double (Given)
23			* Dec spherical coordinate of point to be projected (radians)
24			* raz = double (Given)
25			* RA spherical coordinate of tangent point (radians)
26			* decz = double (Given)
27			* Dec spherical coordinate of tangent point (radians)
28			* xi = double * (Returned)
29			* First rectangular coordinate on tangent plane (radians)
30			* eta = double * (Returned)
31			* Second rectangular coordinate on tangent plane (radians)
32			* j = int * (Returned)
33			* status: 0 = OK, star on tangent plane
34			* 1 = error, star too far from axis
35			* 2 = error, antistar on tangent plane
36			* 3 = error, antistar too far from axis
37
38			* Description:
39			* Projection of spherical coordinates onto tangent plane:
40			* "gnomonic" projection - "standard coordinates"
41
42			* Authors:
43			* PTW: Pat Wallace (STFC)
44			* TIMJ: Tim Jenness (JAC, Hawaii)
45			* {enter_new_authors_here}
46
47			* History:
48			* 2012-02-08 (TIMJ):
49			* Initial version with documentation taken from Fortran SLA
50			* Adapted with permission from the Fortran SLALIB library.
51			* {enter_further_changes_here}
52
53			* Copyright:
54			* Copyright (C) 1996 Rutherford Appleton Laboratory
55			* Copyright (C) 2012 Science and Technology Facilities Council.
56			* All Rights Reserved.
57
58			* Licence:
59			* This program is free software: you can redistribute it and/or
60			* modify it under the terms of the GNU Lesser General Public
61			* License as published by the Free Software Foundation, either
62			* version 3 of the License, or (at your option) any later
63			* version.
64			*
65			* This program is distributed in the hope that it will be useful,
66			* but WITHOUT ANY WARRANTY; without even the implied warranty of
67			* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
68			* GNU Lesser General Public License for more details.
69			*
70			* You should have received a copy of the GNU Lesser General
71			* License along with this program. If not, see
72			* .
73
74			* Bugs:
75			* {note_any_bugs_here}
76			*-
77			*/
78
79			#include "pal.h"
80			#include
81
82			void
83	0		palDs2tp ( double ra, double dec, double raz, double decz,
84			double xi, double eta, int *j ) {
85
86			const double TINY = 1.0e-6;
87
88			double cdec;
89			double sdec;
90			double radif;
91			double cdecz;
92			double denom;
93			double sdecz;
94			double cradif;
95			double sradif;
96
97			/* Trig functions */
98	0		sdecz = sin(decz);
99	0		sdec = sin(dec);
100	0		cdecz = cos(decz);
101	0		cdec = cos(dec);
102	0		radif = ra - raz;
103	0		sradif = sin(radif);
104	0		cradif = cos(radif);
105
106			/* Reciprocal of star vector length to tangent plane */
107	0		denom = sdec * sdecz + cdec * cdecz * cradif;
108
109			/* Handle vectors too far from axis */
110	0	0	if (denom > TINY) {
111	0		*j = 0;
112	0	0	} else if (denom >= 0.) {
113	0		*j = 1;
114			denom = TINY;
115	0	0	} else if (denom > -TINY) {
116	0		*j = 2;
117			denom = -TINY;
118			} else {
119	0		*j = 3;
120			}
121
122			/* Compute tangent plane coordinates (even in dubious cases) */
123	0		xi = cdec sradif / denom;
124	0		eta = (sdec cdecz - cdec * sdecz * cradif) / denom;
125
126	0		return;
127			}