Name

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DAO_VALUE

Purpose

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Returns the value of a DAOPHOT point-spread function at a set of points.

Explanation

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The value of the point-spread function is the sum of a
two-dimensional integral under a bivariate Gaussian function, and
a value obtained by interpolation in a look-up table. DAO_VALUE will
optionally compute the derivatives wrt X and Y

Calling Sequence

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Result = DAO_VALUE( xx, yy, gauss, psf, [ dvdx, dvdy ] )

Inputs

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XX,YY - the real coordinates of the desired point relative
to the centroid of the point-spread function.
GAUSS - 5 element vector describing the bivariate Gaussian
GAUSS(0)- the peak height of the best-fitting Gaussian profile.
GAUSS(1,2) - x and y offsets from the centroid of the point-spread
function to the center of the best-fitting Gaussian.
GAUSS(3,4) - the x and y sigmas of the best-fitting Gaussian.
PSF - a NPSF by NPSF array containing the look-up table.

Outputs

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    RESULT - the computed value of the point-spread function at
            a position XX, YY relative to its centroid (which
            coincides with the center of the central pixel of the
            look-up table).

Optional Outputs

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      DVDX,DVDY - the first derivatives of the composite point-spread
            function with respect to x and y.

Notes

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  although the arguments XX,YY of the function DAO_VALUE
are relative to the centroid of the PSF, the function RINTER which
DAO_VALUE calls requires coordinates relative to the corner of the
array (see code).

Procedures Called

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DAOERF, RINTER()

Revison History

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Adapted to IDL by B. Pfarr, STX, 11/17/87 from 1986 STSDAS version
of DAOPHOT
Converted to IDL V5.0 W. Landsman September 1997