slaPcd -

SYNOPSYS

PARAMETERS

double disco

double *x

double *y

DESCRIPTION

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

Given

     disco    double      pincushion/barrel distortion coefficient
     x,y      double      tangent-plane coordinates

Returned

     *x,*y    double      distorted coordinates

Notes

   1)  The distortion is of the form rp = r*(1 + c*r2), 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

           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, slaUnpcd, which performs
        an approximately inverse operation.

  P.T.Wallace   Starlink   15 July 1993

SEE ALSO

• slalib.3