v.perturb(1grass) GRASS GIS User's Manual v.perturb(1grass)
NAME
v.perturb - Random location perturbations of vector points.
KEYWORDS
vector, geometry, statistics, random, point pattern, level1
SYNOPSIS
v.perturb
v.perturb --help
v.perturb [-b] input=name [layer=string] output=name [distribu-
tion=string] parameters=float[,float,...] [minimum=float] [seed=in-
teger] [--overwrite] [--help] [--verbose] [--quiet] [--ui]
Flags:
-b
Do not build topology
Advantageous when handling a large number of points
--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 vector map
Or data source for direct OGR access
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
output=name [required]
Name for output vector map
distribution=string
Distribution of perturbation
Options: uniform, normal
Default: uniform
parameters=float[,float,...] [required]
Parameter(s) of distribution
If the distribution is uniform, only one parameter, the maximum, is
needed. For a normal distribution, two parameters, the mean and
standard deviation, are required.
minimum=float
Minimum deviation in map units
Default: 0.0
seed=integer
Seed for random number generation
Default: 0
DESCRIPTION
v.perturb reads a vector map of points and writes the same points but
perturbs the eastings and northings by adding either a uniform or nor-
mal delta value. Perturbation means that a variating spatial deviation
is added to the coordinates.
NOTES
The uniform distribution is always centered about zero. The associated
parameter is constrained to be positive and specifies the maximum of
the distribution; the minimum is the negation of that parameter. Do
perturb into a ring around the center, the minimum parameter can be
used.
Usually, the mean (first parameter) of the normal distribution is zero
(i.e., the distribution is centered at zero). The standard deviation
(second parameter) is naturally constrained to be positive.
Output vector points are not guaranteed to be contained within the cur-
rent geographic region.
EXAMPLES
Random, uniformly distributed selection
To create a random, uniformly distributed selection of possible new
points with a radius of 100,000 map units, use the following command:
v.perturb input=comm_colleges output=uniform_perturb parameters=100000
Your map should look similar to this figure:
Figure: Map showing the actual community college points and uniformly
random chosen points.
Normal distributed selection
For a normal distribution with a mean of 5000 and standard deviation of
2000, use the following command:
v.perturb input=comm_colleges output=normal_perturb distribution=normal parameters=5000,2000
Figure: Map showing the actual community college points and normally
random chosen and colored points. Notice that each point is closer to
the original point.
Normal distributed selection with a minimum value
In order to include a minimum value of 500, use the following command:
v.perturb input=comm_colleges output=min_perturb distribution=normal parameters=100000,1000 minimum=500
SEE ALSO
v.random, v.univar
AUTHOR
James Darrell McCauley
when he was at: Agricultural Engineering Purdue University
Random number generators originally written in FORTRAN by Wes Peterson
and translated to C using f2c.
SOURCE CODE
Available at: v.perturb source code (history)
Accessed: unknown
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GRASS 7.8.7 v.perturb(1grass)
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