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.

SEE ALSO

vigcompute