NAME
v.random - Generates random 2D/3D vector points.
KEYWORDS
vector,
sampling,
statistics,
random,
point pattern
SYNOPSIS
v.random
v.random --help
v.random [-zab] output=name npoints=integer [restrict=name] [layer=string] [cats=range] [where=sql_query] [zmin=float] [zmax=float] [seed=integer] [column=name] [column_type=string] [--overwrite] [--help] [--verbose] [--quiet] [--ui]
Flags:
- -z
- Create 3D output
- -a
- Generate n points for each individual area
- -b
- Do not build topology
- --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:
- output=name [required]
- Name for output vector map
- npoints=integer [required]
- Number of points to be created
- restrict=name
- Name of input vector map
- Restrict points to areas in input vector
- layer=string
- Layer number or name ('-1' for all layers)
- A single vector map can be connected to multiple database tables. This number determines which table to use. When used with direct OGR access this is the layer name.
- Default: -1
- cats=range
- Category values
- Example: 1,3,7-9,13
- where=sql_query
- WHERE conditions of SQL statement without 'where' keyword
- Example: income < 1000 and inhab >= 10000
- zmin=float
- Minimum z height (needs -z flag or column name)
- Default: 0.0
- zmax=float
- Maximum z height (needs -z flag or column name)
- Default: 0.0
- seed=integer
- The seed to initialize the random generator. If not set the process ID is used
- column=name
- Name of column for z values
- Writes z values to column
- column_type=string
- Type of column for z values
- Options: integer, double precision
- Default: double precision
v.random randomly generates vector points within the
current region using the selected random number generator.
v.random can generate also 3D vector points or
write random value to attribute table. Point height range or
attribute value range is controlled by specifying zmin and zmax values.
Both z values are included in range (zmin <= z <= zmax).
Generated random attribute value type can be controlled by column
data type. Use INTEGER column type for integers and
DOUBLE PRECISION for floating point numbers. Integer values are
calculated by rounding random floating point number.
To produce repeatable results a random seed can be set using the
option seed.
If an input vector map with areas is specified, the location of
random points is restricted to the selected areas. By default, the
requested number of points are distributed across all areas.
If the -a flag is given, the requested number of points is
generated for each individual area. For example, if 20 points should be
generated and the input map has 100 individual areas, 2000 points will
be generated in total.
All examples use the North Carolina sample dataset.
Generate 20 random points with binary attribute (only 0 or 1):
v.random output=binary_random npoints=20 zmin=0 zmax=1 column='binary INTEGER'
Generate 20 random 3D points using a specific random seed:
v.random seed=52 output=height_random npoints=40 zmin=110 zmax=170 -z

Random points with different X, Y, and Z coordinates
Get 20 random samples from raster map:
g.region -p raster=elevation
v.random output=random_samples npoints=20
v.db.addtable map=random_samples layer=1 columns='cat INTEGER, sample DOUBLE PRECISION'
v.what.rast vector=random_samples raster=elevation@PERMANENT layer=1 column=sample
Generate 20 random points and sample attribute data from geology (vector) map:
g.region -p vector=geology
v.random output=random_samples npoints=20
v.db.addtable map=random_samples layer=1 columns='cat integer, geology varchar(100)'
v.what.vect vector=random_samples layer=1 column=geology \
qvector=geology@PERMANENT qlayer=1 qcolumn=label
Generate 20 random points in forested areas
g.region -p raster=landclass96
r.to.vect -v input=landclass96 output=landclass96 type=area
v.random input=landclass96 output=random_samples npoints=20 \
where="label = 'forest'"
Generate 20 random points in each forest patch
g.region -p raster=landclass96
r.to.vect -v input=landclass96 output=landclass96 type=area
v.random input=landclass96 output=random_samples npoints=20 \
where="label = 'forest'" -a
g.region,
r.random,
v.perturb,
v.sample,
v.what.rast,
v.what.vect
James Darrell McCauley
<darrell@mccauley-usa.com>,
when he was at:
Agricultural
Engineering
Purdue University
Last changed: $Date: 2014-12-20 06:05:23 +0100 (Sat, 20 Dec 2014) $
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GRASS Development Team,
GRASS GIS 7.0.3 Reference Manual