idlastro / FITS Astrometry and Calibration: UPDATE_DISTORT

[Source code]

NAME
UPDATE_DISTORT
PURPOSE
Update SIP nonlinear distortion coefficients for a linear transformation
EXPLANATION
The SIP coefficients can account for nonlinearities in the astrometry
of an astronomical image.    When the image is compressed or expanded
these coefficients must be adjusted in a nonlinear way.
CALLING SEQUENCE
UPDATE_DISTORT, distort, xcoeff, ycoeff
INPUT/OUTPUT
distort - structure giving SIP coefficients.    See extast.pro for 
         description of the SIP distortion structure
xcoeff - 2 element numeric vector describing the linear transformation
          xp = xcoeff[0]*x + xcoeff[1]
xcoeff - 2 element numeric vector describing the linear transformation
          yp = ycoeff[0]*x + ycoeff[1]
METHOD
The procedure TRANSFORM_COEFF is  used to determine how the
coefficients change under the linear transformation.
See example of usage in hrebin.pro
REVISION HISTORY
Written, December 2007            W. Landsman