NAME¶
r.random - Creates a raster map layer and vector point map
containing randomly located points.
KEYWORDS¶
raster, random
SYNOPSIS¶
r.random
r.random help
r.random [-
zidb]
input=
name
[
cover=
name]
n=
number[%]
[
raster_output=
name] [
vector_output=
name]
[--
overwrite] [--
verbose] [--
quiet]
Flags:¶
- -z
-
Generate points also for NULL category
- -i
-
Report information about input raster and exit
- -d
-
Generate vector points as 3D points
- -b
-
Do not build topology in points mode
- --overwrite
-
Allow output files to overwrite existing files
- --verbose
-
Verbose module output
- --quiet
-
Quiet module output
Parameters:¶
- input=name
-
Name of input raster map
- cover=name
-
Name of cover raster map
- n=number[%]
-
The number of points to allocate
- raster_output=name
-
Name for output raster map
- vector_output=name
-
Name for output vector map
DESCRIPTION¶
The program
r.random allows the user to create a raster map layer and/or
a vector points map containing coordinates of points whose locations have been
randomly determined. The program locates these randomly generated vector
points (sites) within the current geographic region and mask (if any), on
non-NULL category value data areas within a user-specified raster map layer.
If the user sets the
-z flag, points will be randomly generated across
all cells (even those with NULL values).
The category values and corresponding category names already associated with the
random point locations in the
input map layer are assigned to these
points in the
raster_output map layer. If the
-z is specified,
then a unique entry is made for the value used where the
input was
NULL. This value is at least 1 less than the smallest value in the
input raster and is given a medium gray color.
NOTES¶
If a
cover raster map is specified and the
cover map contains NULL
(no data) values, these points are suppressed in the resulting
vector_output or
raster_output map.
The
vector_output file created by
r.random contains vector points
that represent the
center points of the randomly generated cells. A
value attribute contains the cell value of the
input raster (or
the assigned value when
-z is used).
If a
cover map is additionally specified, a second column
covervalue is populated with raster values from the
cover map.
If the user sets the
-b flag, vector points are written without topology
to minimize the required resources. This is suitable input to
v.surf.rst and other vector modules.
The user may specify the quantity of random locations to be generated either as
a
positive integer (e.g., 10), or as a
percentage of the raster map
layer's cells (e.g., 10%, or 3.05%). The number of cells considered for
the percentage reflects whether or not the
-z flag was given. Options
are 0-100; percentages less than one percent may be stated as decimals.
Flag
-i prints the raster map's name and location, the total number of
cells under the current region settings, and the number of NULL valued cells
under the current region settings. Then module exits without doing anything.
Useful for deciding on the number of sites to have
r.random create.
WARNING: this feature may be removed in future. Use g.region and
r.report instead.
g.region -p
r.report map=inputmap units=c null=* nsteps=1
To create random vector point locations within some, but not all, non-zero
categories of the input raster map layer, the user must first create a
reclassified raster map layer of the original raster map layer (e.g., using
the GRASS program
r.reclass) that contains only the desired categories,
and then use the reclassed raster map layer as input to
r.random.
EXAMPLES¶
Random vector elevation points sampled from elevation map in the Spearfish
region, result stored in 2D vector map:
g.region rast=elevation.10m -p
r.random elevation.10m vector_output=elevrand n=100
v.db.select elevrand
v.univar elevrand col=value type=point
Random vector elevation points sampled from elevation map in the Spearfish
region with collocated values sampled from landuse map, result stored in 3D
vector map:
g.region rast=elevation.10m -p
r.random -d elevation.10m cover=landcover.30m vector_output=luserand3d n=100
# data output (value: elevation, covervalue: landuse class):
v.db.select luserand3d
cat|value|covervalue
1|1151.406616|81
2|1172.121216|71
3|1183.219604|71
BUGS¶
It's not possible to use the
-i flag and not also specify the
n
parameter.
SEE ALSO¶
g.region
r.reclass
v.random
v.surf.rst
AUTHOR¶
Dr. James Hinthorne, GIS Laboratory, Central Washington University
Modified for GRASS 5.0 by Eric G. Miller
Cover map support by Markus Neteler, 2007
Last changed: $Date: 2010-09-21 15:06:44 +0200 (Tue, 21 Sep 2010) $
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