Help for GTPSWARP

PURPOSE
    uses a single 1024 correlation to shift an image to match another.
The label is changed, so whole pixel shift only.  The image pixels are
not moved or changed at all (see procedure GTMOVE).

Now programmed with imcorner calls to find extent of data in both images.  The
corners of data in the second image are mapped back to the first image and
overlaid with the extent of data in the first image.  The footprint of the 
fft correlation is set to maximal size inside of data.  This can fail somewhat
due to mapping discrepancy between the two images or curved edges of data.

If subpix is set to 1, then the subpixel offset is placed into columns
(14,15) of the ibis file named by parameter ibistmp.

Program now modified to perform four correlations and takes the highest correlation
value of the four.

CALL
  
  
OPERATION


PERFORMANCE

Restrictions
The input and reference images must have VICAR GeoTIFF labels.
They must have the same mapping projections (but not necessarily scale),
or really close.
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Original Programmer: A. L. Zobrist, 25 Aug, 2010
Current Cognizant Programmer: A. L. Zobrist

REVISIONS
Last change by: A. L. Zobrist, 15 Dec, 2011    "taking best of four correlations"
2022-08-10 B. Crocco afids to opensource (untested)