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