Help for SUBSAMP

PURPOSE:
    A vicar applications program to reduce the size of an image by
an integer aspect ratio. By default it will copy only the top left
hand corner pixel of the input image to the output of the selected 
aspect ratio. 

OPERATION

    This program reduces the size of the input image by a preselected
aspect ratio. It copies the selected pixel from the input image to the
output image. The selected pixel is within the small kernel of the
aspect ratio. If an image is to be reduced by one half in lines and
samples, it will copy the top left hand pixel from the upper leftmost
2x2 kernel in the input image, to the output image. Specifically,
pixel 1,1, of the input image is copied to pixel 1,1 of the output,
pixel 1,3 to pixel 1,2 of the output, pixel 3,3 to pixel 2,2 of the
output, etc. No averaging or interpolation is done.

    The parameter ZOOM chooses a square aspect ratio. Possible values
range from -2 to -20. The value 0 is interpreted to mean that lzoom
and szoom are to be used. The value of -1 is illegal.

    The parameter LZOOM is the zoom in the line direction. Valid values
are -1 to -20.

    The parameter SZOOM is the zoom in the sample direction. Valid values
are -1 to -20.


    The parameter LLOC is the line location in the aspect ratio kernel to use in 
the line direction. Valid values are 1 to 20 (but not larger than the kernel
ratio).

   The parameter SLOC is the sample location in the aspect ratio kernel to use in 
the sample direction. Valid values are 1 to 20 (but not larger than the kernel
ratio).

    This program is complementary to program SIZE. Program size for negative
zooms always selects the top left hand corner when used in 'NOIN mode. The
SUBSAMP algorithm is much like a fortran do loop or c for loop assignment construct.


OPERATION

    The internal format of the data is floating point. The output data set
is in the same format as the input. If the file is not an exact multiple of
the zoom factor, it will truncate the last line and sample. For example,
if the size of the image is 111,111 and zoom=-1 then the output will be 27,27.


RESTRICTIONS

    1) This program does not preserve Map Projection label geometry.
    2) This program does not work on multiband images
    3) Maximum image size is 19000 x 19000. This is a 32-bit Linux
        limitation. Max size in cartlab is 20000 x 20000 but that
        is not a 64-bit Linux limitation under gfortran 4.6.3 

Note: For delivery to MIPL have to work in both 32-bit and 64-bit versions
    03 Jul 2012 - R. J. Bambery - Reduced max image size from 20000 x 20000
                to 19000 x 19000 for 32-bit linux gfortran 4.1.2
                gives an immediate message:
            [TAE-PRCSTRM] Abnormal process termination; process status code = 9.;
               if dimensions 20000 x 20000.
                larger dimensions OK for gfortran 4.6.3 on 64-bit linux


PROGRAM HISTORY:

Written by: Ray Bambery, 09 November 2010
Cognizant programmer: Ray Bambery
Revision history:

  2010-11-09 R. J. Bambery - Initial release.
  2011-05-10 R. J. Bammery - Removed all warning messages from 
                             gfortran 4.4.4 compiler.
  2012-07-03 R. J. Bambery - Created internal note to reduce internal image
                             dimensions to 19000 x 19000 in delivery to MIPL
                             from whatever dimensions cartlab uses.
  2016-07-03 W. L. Bunch - Migrated to MIPL.