Apply 2-dimensional pincushion/barrel distortion
A PcdMap is specified by giving this distortion coefficient and the coordinates of the centre of the radial distortion. The forward transformation of a PcdMap applies the distortion:
RD = R $\ast $ ( 1 $+$ C $\ast $ R $\ast $ R )
where R is the undistorted radial distance from the distortion centre (specified by attribute PcdCen), RD is the radial distance from the same centre in the presence of distortion, and C is the distortion coefficient (given by attribute Disco).
The inverse transformation of a PcdMap removes the distortion produced by the forward transformation. The expression used to derive R from RD is an approximate inverse of the expression above.
Disco: PcdMap pincushion/barrel distortion coefficient
PcdCen(axis): Centre coordinates of pincushion/barrel distortion