NAME

       r.patch   -  Creates  a composite raster map layer by using known category values from one
       (or more) map layer(s) to fill in areas of "no data" in another map layer.

KEYWORDS

       raster, geometry

SYNOPSIS

       r.patch
       r.patch help
       r.patch [-qz] input=name[,name,...] output=name  [--overwrite]  [--verbose]  [--quiet]

   Flags:
       -q
           Quiet

       -z
           Use zero (0) for transparency instead of NULL

       --overwrite
           Allow output files to overwrite existing files

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       input=name[,name,...]
           Name of raster maps to be patched together

       output=name
           Name for resultant raster map

DESCRIPTION

       The GRASS program r.patch allows the  user  to  build  a  new  raster  map  the  size  and
       resolution  of the current region by assigning known data values from input raster maps to
       the cells in this region.  This is done by filling in "no data" cells, those that  do  not
       yet contain data, contain NULL data, or, optionally contain 0 data, with the data from the
       first input map.  Once this is done the remaining holes are filled in by  the  next  input
       map,  and  so on.  This program is useful for making a composite raster map layer from two
       or more adjacent map layers, for filling in "holes" in a raster map layer's data (e.g., in
       digital  elevation  data),  or  for updating an older map layer with more recent data. The
       current geographic region definition and mask settings are respected.

       The first name listed in the string input=name,name,name, ... is the name of the first map
       whose  data  values  will  be  used  to fill in "no data" cells in the current region. The
       second through last input name maps will be used, in order, to supply data values for  for
       the remaining "no data" cells.

EXAMPLE

       Below,  the  raster map layer on the far left is patched with the middle (patching) raster
       map layer, to produce the composite raster map layer on the right.
         1 1 1 0 2 2 0 0    0 0 1 1 0 0 0 0    1 1 1 1 2 2 0 0
         1 1 0 2 2 2 0 0    0 0 1 1 0 0 0 0    1 1 1 2 2 2 0 0
         3 3 3 3 2 2 0 0    0 0 0 0 0 0 0 0    3 3 3 3 2 2 0 0
         3 3 3 3 0 0 0 0    4 4 4 4 4 4 4 4    3 3 3 3 4 4 4 4
         3 3 3 0 0 0 0 0    4 4 4 4 4 4 4 4    3 3 3 4 4 4 4 4
         0 0 0 0 0 0 0 0    4 4 4 4 4 4 4 4    4 4 4 4 4 4 4 4
        Switching the patched and the patching raster map layers produces the following results:
         0 0 1 1 0 0 0 0    1 1 1 0 2 2 0 0    1 1 1 1 2 2 0 0
         0 0 1 1 0 0 0 0    1 1 0 2 2 2 0 0    1 1 1 1 2 2 0 0
         0 0 0 0 0 0 0 0    3 3 3 3 2 2 0 0    3 3 3 3 2 2 0 0
         4 4 4 4 4 4 4 4    3 3 3 3 0 0 0 0    4 4 4 4 4 4 4 4
         4 4 4 4 4 4 4 4    3 3 3 0 0 0 0 0    4 4 4 4 4 4 4 4
         4 4 4 4 4 4 4 4    0 0 0 0 0 0 0 0    4 4 4 4 4 4 4 4

NOTES

       Frequently, this program is used to patch together adjacent map  layers  which  have  been
       digitized  separately.   The  program  v.mkgrid  can  be  used to make adjacent maps align
       neatly.

       The user should check the current geographic region settings before  running  r.patch,  to
       ensure  that the region boundaries encompass all of the data desired to be included in the
       composite map and to ensure that the region resolution is the resolution  of  the  desired
       data.  To  set  the geographic region settings to one or several raster maps, the g.region
       program can be used:
       g.region rast=map1[,map2[,...]]

       Use of r.patch is generally followed by use of the GRASS programs g.remove  and  g.rename;
       g.remove  is used to remove the original (un-patched) raster map layers, while g.rename is
       used to then assign to the newly-created composite (patched) raster map layer the name  of
       the original raster map layer.

       r.patch creates support files for the patched, composite output map.

EXAMPLE

       Create a list of maps matching a pattern, extend the region to include them all, and patch
       them together to create a mosaic. Overlapping maps will be used in the order listed.
       MAPS=`g.mlist type=rast sep=, pat="map_*"`
       g.region rast=$MAPS
       r.patch in=$MAPS out=mosaic

SEE ALSO

       g.region, g.remove, g.rename, r.mapcalc, r.support, v.mkgrid

AUTHOR

       Michael Shapiro, U.S. Army Construction Engineering Research Laboratory
       -z flag by Huidae Cho

       Last changed: $Date: 2011-11-08 03:29:50 -0800 (Tue, 08 Nov 2011) $

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