idlastro / FITS Astrometry and Calibration: TPV_EVAL

[Source code]

NAME
TPV_EVAL
PURPOSE
Compute distorted coordinates given TPV (Tangent + PV_ polynomial) 
coefficients.
EXPLANATION
See http://fits.gsfc.nasa.gov/registry/tpvwcs.html for the TPV convention
This distortion convention is used by the SCAMP software 
( http://www.astromatic.net/software/scamp ) though SCAMP does not 
include the '-TPV' in the CTYPE keyword.
The coefficients are passed via common block.    This is because this
routine is called by the intrinisc BROYDEN() function in AD2XY, and 
common blocks are the only way to pass parameters to the user supplied 
function in BROYDEN().  
CALLING SEQUENCE
res = TPV_EVAL(xy)   
INPUTS
xy - 2 elements vector giving the undistorted X,Y position  
OUTPUTS
res - 2 element vector giving the distorted position 
COMMON BLOCKS
common broyden_coeff,pv1,ycoeff
pv1, YCOEFF are both vectors giving the TPV coefficients
REVISION HISTORY
Written   W. Landsman                  Dec 2013
Correct several typos for 4th power terms    M. Sullivan  Mar 2014