v.perturb(1grass) | Grass User's Manual | v.perturb(1grass) |
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]
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 16:11:10 +0100 (Sun, 07 Jan 2018) $
Available at: v.perturb source code (history)
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