Level 2 Help for GTWARP

Input file name.  This parameter is input as:
     INP=innam
where "innam" is the input file name.

Output file name. This parameter is input as:
     OUT=outnam
where:
"outnam" is the output file name.VARI OUT

reference file name. This parameter is input as:
     REF=refnam
where:
"refnam" is the reference file name.

This is a VICAR image that has a GeoTIFF label to specify a mapping.
It could be an image of a geographic area, or it could be a single 
pixel image that serves as the holder of the GeoTIFF mapping information
only.  In the latter case only the 'coverinp case would make sense.

This parameter has three valid keyword values: NOIN and BILIN.

NOIN means no interpolation.   The default method (used when neither keyword 
is specified) for computing the
DN values of the output picture is to use a bi-linear interpolation
on the four nearest neighbors in the input picture.  With NOIN, the
value of the nearest point is simply used.
For example, say a point in the output picture was determined
to have come from point (R,P) in the input picture.  Since R and P
are real values, we must somehow calculate a DN value for that
point.  Take IR and IP as the truncated values.  We then have
          VAL1                                 VAL2
           *                                    *
         (IR,IP)                              (IR,IP+1)
                     POINT
                       *
                     (R,P)
          VAL3                                 VAL4
           *                                    *
         (IR+1,IP)                           (IR+1,IP+1)
Here, POINT is the result of a bilinear interpolation using
VAL1, VAL2, VAL3, and VAL4.
If NOIN is specified, then POINT would be VAL1, the nearest
neighbor.

ZNOIN specifies that a four-point interpolation is done except
when one or more of the points used has a value equal to zero. 
In that case the nearest method is used.
This allows preparation of sharp edges (no interpolation rolloff)
for mosaicking.

     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 has
     no effect in this case.
	   

Added width of gores for 'coverinp case only.  This number of pixel
columns or rows is added to all four sides.  Zero fill is used.