Name

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    UPDATE_DISTORT

Purpose

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    Update SIP nonlinear distortion coefficients for a linear transformation

Explanation

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    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

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    UPDATE_DISTORT, distort, xcoeff, ycoeff

Input/output

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    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

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    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

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    Written, December 2007 W. Landsman