.help seepsf May00 noao.digiphot.daophot
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NAME
seepsf -- convert a sampled PSF lookup table to a PSF image
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USAGE
seepsf psfimage image
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PARAMETERS
.ls psfimage
The list of input PSF images computed by the PSF task. Each PSF image consists
of the parameters of a 2D analytic function stored in the image header and an
optional sampled lookup table of residuals from that fit stored in the image
pixels.
.le
.ls image
The list of output PSF images consisting of the sum of the analytic function
and the residuals in the lookup table. There must be one output PSF image for
each input PSF image.
.le
.ls dimension = INDEF
The dimensions of the output PSF image. By default \fIimage\fR is a 2D image
with dimensions of N by N where N = 2 * nint (psfrad / scale)  + 1 with the
same scale as the original image from which \fIpsfimage\fR was derived.
\fIPsfrad\fR is the PSF fitting radius stored in the \fIpsfimage\fR image
header parameter "PSFRAD". \fIScale\fR is the image scale stored in the image
header parameter "SCALE".
.le
.ls xpsf = INDEF
The x coordinate of the output PSF. \fIXpsf\fR is only used if \fIpsfimage\fR
was computed with the variable PSF parameter \fIvarorder\fR in the DAOPARS task
set to > 0.
.le
.ls ypsf = INDEF
The y coordinate of the output PSF. \fIYpsf\fR is only used if \fIpsfimage\fR
was computed with the variable PSF parameter \fIvarorder\fR in the DAOPARS task
set to > 0.
.le
.ls magnitude = INDEF
The intensity scale of the output PSF. By default the intensity scale is set by
the magnitude of the first star used by the PSF task to compute \fIpsfimage\fR.
This parameter is stored in the keyword "PSFMAG" in \fIpsfimage\fR.
.le
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DESCRIPTION
SEEPSF takes the input PSF \fIpsfimage\fR computed by the PSF task, consisting
of the parameters of a 2D analytic function stored in the image header and an
optional lookup table of residuals from the fit stored in the image pixels, and
computes an output PSF, \fIimage\fR, consisting of the sum of the analytic
function and the residuals.

By default \fIimage\fR is a 2D image of dimensions N by N where N = 2 * nint
(psfrad) + 1 and the scale of \fIimage\fR is the same as the scale of the
original image from which \fIpsfimage\fR  was derived. If \fIdimension\fR is
greater or less than N then the output PSF is block-averaged or subsampled with
respect to the original image. \fIPsfrad\fR is the value of the psf radius
parameter in the task DAOPARS used to compute \fIpsfimage\fR and is stored in
the \fIpsfimage\fR header parameter "PSFRAD".

If \fIpsfimage\fR was computed with the variable PSF parameter \fIvarorder\fR
set to > 0, then \fIimage\fR is computed at a point (xpsf, ypsf) defined
relative to the original image.  By default \fIimage\fR is computed at the
centroid of the PSF defined by the \fIpsfimage\fR header parameters "XPSF"
and "YPSF".

The intensity scale of \fIimage\fR is determined by the value of \fImagnitude\fR
relative to the magnitude of the PSF. By default the output PSF has the
magnitude of the first PSF star stored in the \fIpsfimage\fR header parameter
"PSFMAG".

SEEPSF is most commonly used for visualizing the PSF in image scale coordinates
and checking the form of any variability as a function of position. However
\fIimage\fR can also be used as input to other image processing program, for
example it might be used as the kernel in a convolution operation.

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EXAMPLES

1. Compute the output PSF in image scale coordinates of PSF function
for image dev$ypix.

.nf
    da> seepsf ypix.psf.3 ypixpsf
.fi

2. Compute the output PSF in image scale coordinates of the variable
PSF for the image m92b at position (113.63,50.48) pixels relative to the
original image.

.nf
    da> seepsf m92b.psf.2 m92psf xpsf=113.63 ypsf=50.48
.fi

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TIME REQUIREMENTS
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BUGS
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SEE ALSO
datapars,daopars,psf
.endhelp