Ubuntu Manpage: r.patch - Creates a composite raster map layer by using known category values from one (or more) map

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Provided by: grass-doc_7.0.3-1build1_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, mosaicking, merge, patching

SYNOPSIS

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

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

       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

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

       output=name [required]
           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 of filling areas
       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.  The example assumes zero values to  be  treated  as
       NULLs (-z flag).
         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 raster=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.

Number of raster maps to be processed is given by the limit of the operating system. For example, both
the hard and soft limits are typically 1024. The soft limit can be changed with e.g. ulimit -n 1500
(UNIX-based operating systems) but not higher than the hard limit. If it is too low, you can as superuser
add an entry in
/etc/security/limits.conf
# <domain> <type> <item> <value>
your_username hard nofile 1500
This would raise the hard limit to 1500 file. Be warned that more files open need more RAM. See also the
Wiki page Hints for large raster data processing.

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.list type=raster sep=, pat="map_*"`
       g.region raster=$MAPS
       r.patch in=$MAPS out=mosaic

AUTHOR

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

       Last changed: $Date: 2015-10-09 18:55:34 +0200 (Fri, 09 Oct 2015) $

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