Help for GTWARP

PURPOSE
     GTWARP reads the GeoTIFF label of a "master" or "reference" image,
     then reads the GeoTIFF label of the input image.  It calculates
     a set of GEOMV parameters from these and then calls GEOMV to warp
     the input image to match the mapping of the "reference" image.
     
     1.  The keyword 'coverinp causes the procedure to map all of the
     input image to an output image that will just contain it.   The
     keyword gorewid allows the user to specify a zero-filled margin
     to make the output a little larger (or negative trims smaller).
	
     2.  The keyword 'coverref causes the procedure to map the input
     image to an output image that exactly matches the "reference" image.
     Some parts of the input can be lost, or huge areas of zero-fill
     could be added to make the images match.  The gorewid keyword
     enlarges the output on all 4 sides by the specified number of pixels
     while keeping the correct mapping.
	   
CALL
     gtwarp INPUT OUTPUT REF '(QUALIFIERS) PARAMS
  WHERE:
     INPUT          is the input data set (must have a GeoTIFF label).
     OUTPUT         is the output data set (will have a GeoTIFF label).
     REF            is the reference data set (must have a GeoTIFF label).
     QUALIFIERS     consist of any of the following keywords:
          COVERINP         smallest output that covers the input geographic area
          COVERREF         output exactly matches the reference image.
     PARAMS         interp,nah,nav,gorewid.

  
OPERATION

First, for the 'coverinp case only, the procedure calculates the
extrema of the input in the output pixel space.  For the 'coverref
case, the extrema are the boundaries of the reference image.

Then the procedure calculates (in an ibis file) a grid that is
rectangular in the output space using the extrema calculated above.
Then new columns are calculated using the GeoTIFF map projections
in the labels of the input and reference images yielding the grid
in the input image.  Then GEOMV is called to calculate the result.

PERFORMANCE

The time will consist of the IBIS file grid generation and mapping
which could be minutes for a 1000 x 1000 grid plus the GEOMV time.
See the GEOMV document for GEOMV timing (a 4000 by 4000 image was
transformed by a 500 x 500 grid in 99 seconds on a SPARCstation 20.
Reducing the grid to 30 x 30 cut the time to 39 seconds.  This shows
that the use of a large grid doesn't penalize the time too much, 1999).

Restrictions
------------

The input and reference images must have GeoTIFF labels.


Original Programmer: A. L. Zobrist, 02 Mar, 2000
Corrected June 8, 2010 znoin corrections, cubic interpolations added. ALZ
Current Cognizant Programmer: A. L. Zobrist