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v.perturb(1) Grass User's Manual v.perturb(1)

v.perturb - Random location perturbations of vector points.

vector, geometry, statistics, random, point pattern, level1

v.perturb
 
v.perturb --help
 
v.perturb [-b] input=name [layer=string] output=name [distribution=string] parameters=float[,float,...] [ minimum=float] [ seed=integer] [--overwrite] [-- help] [--verbose] [--quiet] [--ui]

-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

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

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 normal delta value. Perturbation means that a variating spatial deviation is added to the coordinates.

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 current geographic region.

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.

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.

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

v.random, v.univar

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.
Last changed: $Date: 2018-01-07 16:12:07 +0100 (Sun, 07 Jan 2018) $

Available at: v.perturb source code (history)
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© 2003-2018 GRASS Development Team, GRASS GIS 7.4.3 Reference Manual
GRASS 7.4.3

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