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## NAME

vigfit -- Smooth GHRS vignetting function.

## USAGE

`vigfit input mask output1 output2 outtable `

## DESCRIPTION

This routine computes a smooth GHRS vignetting function by computing
a least squares cubic spline through an raw input vignetting function
computed by the routine `vigcompute`. The number of spline nodes can be
specified and the nodes may be unequally spaced. The output vignetting
function
is normalized to unity at photocathode sample position 280.

## PARAMETERS

- input [file name]
- Name of the raw vignetting image computed by routine
`vigcompute`.

- mask [file name]
- Optional data mask for
`input`. If set to "" (i.e., no file name is supplied), the least squares spline is fit to all data points.

- output= "fit" [file name]
- This image contains the least squares spline fit, computed at all points in the input observation and is thus suitable for overplotting on the input data for fit evaluation.

- output= "vig" [file name]
- This image contains the output vignetting function (the least squares spline
normalized to unity at
`sample=280`) evaluated at all sample locations from 0.0 to 560.0 with a step size of 1.0 making it a 561 point image.

- outtable = "nodes" [file name]
- Name of the output table to contain the cubic spline node positions and
values. It will have columns
`SAMPLE`and`VALUE`.

- (nodes = 10) [integer, min=3, max=20]
- Number of equally spaced least square spline nodes. It is ignored if
an
`intable`file name is supplied.

- (niter = 10) [integer, min=1, max=200]
- Number of least squares iterations to perform.

- (intable = " ") [file name]
- If an
`intable`value is supplied (i.e., it is not equal to ""), the input node positions are taken from table column`SAMPLE`. This table should be used to specify node positions if unequally spaced nodes are used. The output table,`outtable`, from a previous run of`vigfit`can be edited to adjust node positions and then used as input to the next try.

- (template = "hrs$templates/hrsvig") [file name]
- Name of a template image for the output vignetting image
`output2`.

## EXAMPLES

1. Fit the vignetting function to the raw data image `rawvig` using 13
equally spaced nodes. The image `mask` is used to mask out bad data
points or those corrupted by sharp spectral lines.

hr> vigfit rawvig mask fit vignetting nodetable nodes=13

2. Edit the node table to adjust node positions if
unequally spaced spline nodes are needed. `vigfit` can then be
rerun.

hr> vigfit rawvig mask fit vignetting nodetable2 intable="nodetable"

## BUGS

## REFERENCES

## HELP

For assistance using this or any other tasks, please contact help@stsci.edu or call the help desk at 410-338-1082.