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       r.cross  - Creates a cross product of the category values from multiple raster map layers.


       raster, statistics


       r.cross help
       r.cross [-zq] input=string[,string,...] output=name  [--overwrite]  [--verbose]  [--quiet]

           Non-zero data only

           Run quietly

           Allow output files to overwrite existing files

           Verbose module output

           Quiet module output

           Names of 2-30 input raster maps

           Name for output raster map


       r.cross  creates  an  output  raster  map  layer  representing  all unique combinations of
       category values in the raster input layers (input=name,name,name, ...).  At least two, but
       not  more than ten, input map layers must be specified.  The user must also specify a name
       to be assigned to the output raster map layer created by r.cross.


       The program will be run non-interactively if the user specifies the names of between  2-10
       raster  map  layers  be  used as input, and the name of a raster map layer to hold program

       With the -z flag zero data values are not crossed.  This means that  if  a  zero  category
       value  occurs in any input data layer, the combination is assigned to category zero in the
       resulting map layer, even if other data layers contain  non-zero  data.   In  the  example
       given above, use of the -z option would cause 3 categories to be generated instead of 5.

       If  the  -z  flag  is not specified, then map layer combinations in which not all category
       values are zero will be assigned a unique category value in the resulting map layer.

       Category values in the new output map layer will be  the  cross-product  of  the  category
       values from these existing input map layers.


       For example, suppose that, using two raster map layers, the following combinations occur:
                 map1   map2
                  0      1
                  0      2
                  1      1
                  1      2
                  2      4
        r.cross would produce a new raster map layer with 5 categories:
                 map1   map2   output
                  0      1       1
                  0      2       2
                  1      1       3
                  1      2       4
                  2      4       5
         Note:  The  actual category value assigned to a particular combination in the result map
       layer is dependent on the order in which the combinations occur in  the  input  map  layer
       data  and  can  be  considered essentially random.  The example given here is illustrative


       The category file created for the output raster map layer describes  the  combinations  of
       input  map layer category values which generated each category.  In the above example, the
       category labels would be:
                 category   category
                 value      label
                    1       layer1(0) layer2(1)
                    2       layer1(0) layer2(2)
                    3       layer1(1) layer2(1)
                    4       layer1(1) layer2(2)
                    5       layer1(2) layer2(4)
        A random color table is also generated for the output map layer.


       When run non-interactively, r.cross will not protect existing files in the user's  mapset.
       If  the user specifies an output file name that already exists in his mapset, the existing
       file will be overwritten by the new r.cross output.


       r.covar, r.stats


       Michael Shapiro, U.S. Army Construction Engineering Research Laboratory

       Last changed: $Date: 2008-08-11 20:34:28 -0700 (Mon, 11 Aug 2008) $

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