idlastro / DAOPHOT-Type Photometry Procedures: DAO_VALUE

[Source code]

NAME
DAO_VALUE
PURPOSE
Returns the value of a DAOPHOT point-spread function at a set of points.
EXPLANATION
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
Result = DAO_VALUE( xx, yy, gauss, psf, [ dvdx, dvdy ] )
INPUTS
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
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
DVDX,DVDY - the first derivatives of the composite point-spread
      function with respect to x and y.
NOTES
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
DAOERF, RINTER()
REVISON HISTORY
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