r.random(1grass) GRASS GIS User's Manual r.random(1grass)
NAME
r.random - Creates a raster map layer and vector point map containing
randomly located points.
KEYWORDS
raster, sampling, vector, random, level1
SYNOPSIS
r.random
r.random --help
r.random [-zidb] input=name [cover=name] npoints=number[%]
[raster=name] [vector=name] [seed=integer] [--overwrite]
[--help] [--verbose] [--quiet] [--ui]
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
Do not build topology in points mode
--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 [required]
Name of input raster map
cover=name
Name of cover raster map
npoints=number[%] [required]
The number of points to allocate
raster=name
Name for output raster map
vector=name
Name for output vector map
seed=integer
Seed for rand() function
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 loca-
tions have been randomly determined. The program locates these ran-
domly generated vector points (sites) within the current geographic re-
gion 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 val-
ues).
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 in-
put 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_out-
put 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 topol-
ogy 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 do-
ing 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 de-
sired categories, and then use the reclassed raster map layer as input
to r.random.
EXAMPLES
Random 2D vector elevation points
Random vector elevation points sampled from elevation map in the North
Carolina sample dataset region, result stored in 2D vector map:
g.region raster=elevation -p
r.random elevation vector=elevrand n=100
v.db.select elevrand
v.univar elevrand col=value type=point
Random 3D vector elevation points
Random vector elevation points sampled from elevation map in the North
Carolina sample dataset region with collocated values sampled from lan-
duse map, result stored in 3D vector map:
g.region raster=elevation -p
r.random -d elevation cover=landclass96 vector=luserand3d n=100
# data output (value: elevation, covervalue: landuse class):
v.db.select luserand3d
cat|value|covervalue
1|111.229591|5
2|71.093758|1
3|122.51075|5
4|146.17395|4
...
KNOWN ISSUES
It’s not possible to use the -i flag without specifying the npoints pa-
rameter.
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
SOURCE CODE
Available at: r.random source code (history)
Accessed: unknown
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GRASS 7.8.7 r.random(1grass)
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