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SUBROUTINE slPCD (DISCO,X,Y)
*+
* - - - -
* P C D
* - - - -
*
* Apply pincushion/barrel distortion to a tangent-plane [x,y].
*
* Given:
* DISCO d pincushion/barrel distortion coefficient
* X,Y d tangent-plane coordinates
*
* Returned:
* X,Y d distorted coordinates
*
* Notes:
*
* 1) The distortion is of the form RP = R*(1 + C*R**2), where R is
* the radial distance from the tangent point, C is the DISCO
* argument, and RP is the radial distance in the presence of
* the distortion.
*
* 2) For pincushion distortion, C is +ve; for barrel distortion,
* C is -ve.
*
* 3) For X,Y in units of one projection radius (in the case of
* a photographic plate, the focal length), the following
* DISCO values apply:
*
* Geometry DISCO
*
* astrograph 0.0
* Schmidt -0.3333
* AAT PF doublet +147.069
* AAT PF triplet +178.585
* AAT f/8 +21.20
* JKT f/8 +13.32
*
* 4) There is a companion routine, slUPCD, which performs the
* inverse operation.
*
* P.T.Wallace Starlink 3 September 2000
*
* Copyright (C) 2000 Rutherford Appleton Laboratory
*
* License:
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program (see SLA_CONDITIONS); if not, write to the
* Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
* Boston, MA 02110-1301 USA
*
* Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
*-
IMPLICIT NONE
DOUBLE PRECISION DISCO,X,Y
DOUBLE PRECISION F
F=1D0+DISCO*(X*X+Y*Y)
X=X*F
Y=Y*F
END
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