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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