


                                  - 1 -



       COMMAND

       ccccoooommmmbbbb,,,, ccccoooommmmppppaaaacccctttt ---- ddddaaaattttaaaa rrrreeeedddduuuuccccttttiiiioooonnnn ttttoooooooollllssss

       USAGE

       ccccoooommmmbbbb [----ggggtttt] [_l_g_f_a_c_t_o_r] [_l_t_f_a_c_t_o_r]

       ccccoooommmmppppaaaacccctttt [----ggggtttt] [_l_g_f_a_c_t_o_r] [_l_t_f_a_c_t_o_r]

       DESCRIPTION

       These commands perform simple data reduction operations.
       The ccccoooommmmbbbb command reduces the data by converting longitudes
       or latitudes to void values.  The ccccoooommmmppppaaaacccctttt command reduces
       the data by moving latitudes or longitudes to a smaller
       range.

       The option switches and pitch arguments may be used in
       various combinations provided the number of pitch arguments
       corresponds to the number of switches selected and the order
       of factors is as shown.  The default is ----ggggtttt, which is
       overridden if either option is present.

       ----gggg        Enable erasing or compacting longitudes.  Disables
                 altering latitudes unless ----tttt is present.

       ----tttt        Enable erasing or compacting latitudes.  Disables
                 altering longitudes unless ----gggg is present.

       _l_g_f_a_c_t_o_r  Longitudinal (X axis) reduction factor.

       _l_t_f_a_c_t_o_r  Latitudinal (Y axis) reduction factor.

       Both commands enable you to reduce the density of data
       points defining the surface of the image.  The effect is
       equivalent to obtaining a digitized image using an n-fold
       decrease in the sampling frequency in either latitudinal or
       longitudinal directions.  Every n'th (_f_a_c_t_o_r) longitude or
       latitude of data points is retained.

       Use of the ccccoooommmmppppaaaacccctttt command results in the retained data
       points being shifted by the appropriate number of
       longitudes, latitudes or both so that they occupy a
       contiguous compacted subset of the image space.  In the case
       of the ccccoooommmmbbbb command the retained data points continue to
       occupy their original position in the image space and the
       longitudes or latitudes of intervening data points are
       converted to voids.













                                  - 2 -



       The commands may be used without arguments in which case all
       odd numbered longitudes and latitudes are deleted.

       For the ccccoooommmmppppaaaacccctttt command only, the data set is compressed and
       shifted so as to occupy an image space comprised of
       latitudes and longitudes 0 through 127.  The balance of the
       original image is converted to voids.  Finally, the values
       of llllttttiiiinnnnccccrrrr and llllggggiiiinnnnccccrrrr are doubled in value so that the
       reduced resolution image can be projected into whatever
       context could accept the original image.  The array which
       contains the image, as defined by the variables nnnnlllltttt and nnnnllllgggg
       is not changed.  The image file will not be reduced in size,
       and the image space beyond llllttttmmmmaaaaxxxx and llllggggmmmmaaaaxxxx may be used for
       various purposes.

       To reduce the number of longitudes by a factor of 4 but
       retain the same number of latitudes, the command:

       ccccoooommmmbbbb ----gggg 4444

       will erase (void) all but every 4th longitude, and the
       command:

       ccccoooommmmpppprrrreeeessssssss ----gggg 4444

       copies every 4th longitude into a smaller image.  Either
       image would essentially emulate the results of some other
       sampling regime or system having correspondingly reduced
       latitudinal resolution.

       Conversely, if reduced resolution in the longitudinal
       direction is of interest for some purpose, the command:

       ccccoooommmmbbbb ----tttt 3333

       yields an image in which longitudinal features would be
       defined only one third as well as in the original image.






















