palPcd

Apply pincushion/barrel distortion to a tangent-plane [x,y]

Applies pincushion and barrel distortion to a tangent plane coordinate.

palPcd( double disco, double

*

x, double

*

y );

Pincushion/barrel distortion coefficient.

On input the tangent-plane X coordinate, on output the distorted X coordinate.

On input the tangent-plane Y coordinate, on output the distorted Y coordinate.

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.
For pincushion distortion, C is $+$ ve; for barrel distortion, C is -ve.
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