diff options
Diffstat (limited to 'src/slalib/unpcd.f')
| -rw-r--r-- | src/slalib/unpcd.f | 68 |
1 files changed, 68 insertions, 0 deletions
diff --git a/src/slalib/unpcd.f b/src/slalib/unpcd.f new file mode 100644 index 0000000..9502671 --- /dev/null +++ b/src/slalib/unpcd.f @@ -0,0 +1,68 @@ + SUBROUTINE sla_UNPCD (DISCO,X,Y) +*+ +* - - - - - - +* U N P C D +* - - - - - - +* +* Remove pincushion/barrel distortion from a distorted [x,y] +* to give tangent-plane [x,y]. +* +* Given: +* DISCO d pincushion/barrel distortion coefficient +* X,Y d distorted coordinates +* +* Returned: +* X,Y d tangent-plane 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 "radians" - units of one projection radius, +* which in the case of a photograph is the focal length of +* the camera - 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) The present routine is an approximate inverse to the +* companion routine sla_PCD, obtained from two iterations +* of Newton's method. The mismatch between the sla_PCD and +* sla_UNPCD routines is negligible for astrometric applications; +* to reach 1 milliarcsec at the edge of the AAT triplet or +* Schmidt field would require field diameters of 2.4 degrees +* and 42 degrees respectively. +* +* P.T.Wallace Starlink 1 August 1994 +* +* Copyright (C) 1995 Rutherford Appleton Laboratory +*- + + IMPLICIT NONE + + DOUBLE PRECISION DISCO,X,Y + + DOUBLE PRECISION CR2,A,CR2A2,F + + + + CR2=DISCO*(X*X+Y*Y) + A=(2D0*CR2+1D0)/(3D0*CR2+1D0) + CR2A2=CR2*A*A + F=(2D0*CR2A2*A+1D0)/(3D0*CR2A2+1D0) + X=X*F + Y=Y*F + + END |