FFCROSS-Cross-correlate an image and a flat field (mainly IPCS data)

Description:

This is for use with some flat fields (notably IPCS) where there may be a bodily shift between the flat field and the data. For each cross-section in a given range, this routine calculates the cross-correlation between the flat field and the data. It then calculates the average shift for each cross-section, as determined from the individual cross-correlation. It also sums the individual cross-correlations, and calculates the shift given by that summed cross-correlation. The idea is that the shift determined in this way can then be applied using ISHIFT.

Parameters:

IMAGE

Name of image.

FLAT

Name of flat field.

YSTART

First Y value to be used.

YEND

Last Y value to be used.

XSTART

First X value to be used.

XEND

Last X value to be used.

RECORD

Create file to record cross-correlation?

CROSS

Name of cross-correlation data?

LOG

Log individual cross-section shifts?

Source comments:

 F F C R O S S

 Main body of the Figaro FFCROSS function.  This is for use
 with some flat fields (notably IPCS) where there may be a bodily
 shift between the flat field and the data.  For each
 cross-section in a given range, this routine calculates the
 cross-correlation between the flat field and the data.  It then
 calculates the average shift for each cross-section, as determined
 from the individual cross-correlation.  It also sums the individual
 cross-correlations, and calculates the shift given by that summed
 cross-correlation.  The idea is that the shift determined in this
 way can then be applied using ISHIFT.

 Command parameters -

 IMAGE       (Character) The IMAGE to be compared with
             the flat field.
 FLAT        (Character) The FLAT field to be used.
             The FLAT and IMAGE data arrays should have the same
             dimensions.
 YSTART      (Numeric) The first cross-section to be used.
 YEND        (Numeric) The last cross-section to be used.
 XSTART      (Numeric) Data with an AXIS(1) value less than XSTART
             will be ignored in the cross-correlation.
 XEND        (Numeric) Data with an AXIS(1) value greater than XEND
             will also be ignored.  Note that these values are
             used to determine the channel numbers to be used
             for IMAGE and the same ones will be used for
             FLAT even if FLAT has a  different AXIS(1)
             structure.
 CROSS       (Character) the name of the data structure to hold
             the cross-correlation, if it is to be saved.
             The file created will be cross.dst, and will look
             like an ordinary spectrum - i.e. can be plotted by
             SPLOT, etc.  CROSS is ignored if RECORD is not set.

 Command keywords -

 RECORD      If set, the summed cross-correlation of the two
             images will be recorded as a new data structure.
 LOG         If set, the individual shifts for each cross-
             section will be logged as they are calculated.

 User variables used -

 SHIFT       (Numeric) The relative shift of the two images as
             determined from the summed cross-correlation.
 AVSHIFT     (Numeric) The average shift of the individual
             cross-sections.

                                         KS / CIT 5th Oct 1983