1 /*
2 *+
3 * Name:
4 * palPcd
5
6 * Purpose:
7 * Apply pincushion/barrel distortion to a tangent-plane [x,y]
8
9 * Language:
10 * Starlink ANSI C
11
12 * Type of Module:
13 * Library routine
14
15 * Invocation:
16 * palPcd( double disco, double * x, double * y );
17
18 * Arguments:
19 * disco = double (Given)
20 * Pincushion/barrel distortion coefficient.
21 * x = double * (Given & Returned)
22 * On input the tangent-plane X coordinate, on output
23 * the distorted X coordinate.
24 * y = double * (Given & Returned)
25 * On input the tangent-plane Y coordinate, on output
26 * the distorted Y coordinate.
27
28 * Description:
29 * Applies pincushion and barrel distortion to a tangent
30 * plane coordinate.
31
32 * Authors:
33 * PTW: Pat Wallace (RAL)
34 * TIMJ: Tim Jenness
35 * {enter_new_authors_here}
36
37 * Notes:
38 * - The distortion is of the form RP = R*(1 + C*R**2), where R is
39 * the radial distance from the tangent point, C is the DISCO
40 * argument, and RP is the radial distance in the presence of
41 * the distortion.
42 *
43 * - For pincushion distortion, C is +ve; for barrel distortion,
44 * C is -ve.
45 *
46 * - For X,Y in units of one projection radius (in the case of
47 * a photographic plate, the focal length), the following
48 * DISCO values apply:
49 *
50 * Geometry DISCO
51 *
52 * astrograph 0.0
53 * Schmidt -0.3333
54 * AAT PF doublet +147.069
55 * AAT PF triplet +178.585
56 * AAT f/8 +21.20
57 * JKT f/8 +13.32
58 *
59 * See Also:
60 * - There is a companion routine, palUnpcd, which performs the
61 * inverse operation.
62
63 * History:
64 * 2000-09-03 (PTW):
65 * SLALIB implementation.
66 * 2015-01-01 (TIMJ):
67 * Initial version. Ported from Fortran.
68 * {enter_further_changes_here}
69
70 * Copyright:
71 * Copyright (C) 2000 Rutherford Appleton Laboratory.
72 * Copyright (C) 2015 Tim Jenness
73 * All Rights Reserved.
74
75 * Licence:
76 * This program is free software; you can redistribute it and/or modify
77 * it under the terms of the GNU General Public License as published by
78 * the Free Software Foundation; either version 3 of the License, or
79 * (at your option) any later version.
80 *
81 * This program is distributed in the hope that it will be useful,
82 * but WITHOUT ANY WARRANTY; without even the implied warranty of
83 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
84 * GNU General Public License for more details.
85 *
86 * You should have received a copy of the GNU General Public License
87 * along with this program (see SLA_CONDITIONS); if not, write to the
88 * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
89 * Boston, MA 02110-1301 USA
90
91 * Bugs:
92 * {note_any_bugs_here}
93 *-
94 */
95
96 #include "pal.h"
97
palPcd(double disco,double * x,double * y)98 void palPcd( double disco, double *x, double *y ) {
99 double f;
100
101 f = 1.0 + disco * ( (*x) * (*x) + (*y) * (*y) );
102 *x *= f;
103 *y *= f;
104 }
105
106