Provided by: grass-doc_6.4.3-3_all 
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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