Level 2 Help for GTAPPEND

INP specifies the input data sets.  Up to 48 are allowed.

The SIZE parameter may be used when only a sub-region of each image is to
be concatenated; it has the format SIZE=(SL,SS,NL,NS), where the parameters
are starting line, starting sample, number of lines, and number of samples,
respectively.  SIZE=(1,1,10,10), for example, will cause gtappend to only look
at the first ten samples of each of the first ten lines in each image, when
performing the concatenation. The default (1,1,0,0) means use the whole image.

The SIZE parameter is not allowed in GeoTIFF cases.

INTEGER - Starting line (see SIZE)

INTEGER - Starting sample (see SIZE)

INTEGER - Number of lines (see SIZE)

INTEGER - Number of samples (see SIZE)

As each image is butted, the mappings are checked for whether they
continue smoothly across the seam.  The default tolerance of one
millionth of a pixel allows for a fair amount of numeric error in
the calculations, which should always be carried out in double
precision.

See the main help for other checks on the mapping (coordinate system,
projection, datum, rotation, scale, etc must all be the same).

The default, MAPCK, will do GeoTIFF map checking (or do nothing if there
are no GeoTIFF labels).  Using the other option, NOMAPCK, is useful to
add extra pixels to the bottom of a GeoTIFF image, or to adjoin
an image that is already known to be mapped correctly but doesn't have
a GeoTIFF label.  The first, or top, image must have a correct
GeoTIFF label.

Use if images overlap one pixel, as in DMA DTED.  

The program will strip one pixel between each image, from the topmost
image of each pair.  The extra pixel in the last image is NOT stripped.
So two 601 pixel images will concatenate into a 1201 pixel image.

If geotiff labels are present, the location checking will account for
the overlap pixel.  If the images do not, in fact, have an overlap and
this keyword is used, an error would be reported if the geotiff labels
were present, because there would be a missing pixel.

Bottom line for geotiff labels, if there is not a clean butt or an overlap
of one pixel, you have to use imcopy to cut one of the images or 
featherv to mosaic the images.