Help for GRID

PURPOSE:
   GRID superimposes a grid network on a byte data set.   The grid consists
of evenly spaced horizontal and vertical lines.  Each grid line will have 
long and short tick marks (fiducial marks) somewhat like the long and short
marks on a ruler between the lines for each inch.  The details of the grid are
as follows:

   1.  The intensity of the pixels in the network is given by the 
       intensity parameters. 
   2.  Every BLI lines and samples, a one-pixel-wide line is superimposed
       over the data set.
   3.  A (long) mark of length (2 * LFL + 1) pixels is placed across each 
       grid line every LFS pixels.
   4.  A (short) mark of length (2 * SFL + 1) pixels is placed across each 
       grid line every SFS pixels.

       Remark: Intensity parameters,BLI,LFL,SFL,LFS,SFS are defined in 
               the parameter section in TUTOR mode.
EXECUTION:
   The followings are the possible execution statements for 'GRID'.
 
    1. GRID A B 

       where A is an input data set, B is an output data set.
       This will cause a grid network of intensity 255, aligned with
       the reference marks. The default for GEO is (100,25,5,2,1), 
       meaning:
       a)  The lines of the grid are spaced every 100 pixels.
       b)  The long tick marks are spaced every 25 pixels and are 5
           pixels in length.
       c)  The short tick marks are spaced every 5 pixels and are 3
           pixels in length.

    2. GRID A B SIZE=(1,1,100,100) INT=(0,0,100,0)
   
       This will cause the size of the output data set to be 100 lines
       by 100 samples. And all pixels in the network have resultant
       values which are modulo(255,(original value)+100).


    3. GRID A B INT=(0,200,0,100) GEO=(50,30,5,2,1)
       
       This will cause intensity value in the network specified by
       GEO parameters to be multipled by 2 and then taken modulo 255.
       Since LIMIT parameter is specified, if the resultant value is 
       less than the limit or greater than (255-limit), then it is set
       equal to limit or (255-limit) respectively.
 

    4. GRID A B REP=100 BLI=50

       This will cause a grid network of intensity 255 with the basic
       line interval to be every 50 samples.