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SUBROUTINE sla_PCD (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, sla_UNPCD, which performs
* an approximately inverse operation.
*
* P.T.Wallace Starlink 31 December 1992
*
* Copyright (C) 1995 Rutherford Appleton Laboratory
*-
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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