1v.perturb(1)                GRASS GIS User's Manual               v.perturb(1)
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NAME

6       v.perturb  - Random location perturbations of vector points.
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KEYWORDS

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

12       v.perturb
13       v.perturb --help
14       v.perturb  [-sb]  input=name   [layer=string]   output=name  [distribu‐
15       tion=string]  parameters=float[,float,...]  [minimum=float]   [seed=in‐
16       teger]   [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]
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18   Flags:
19       -s
20           Generate random seed (result is non-deterministic)
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22       -b
23           Do not build topology
24           Advantageous when handling a large number of points
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26       --overwrite
27           Allow output files to overwrite existing files
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29       --help
30           Print usage summary
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32       --verbose
33           Verbose module output
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35       --quiet
36           Quiet module output
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38       --ui
39           Force launching GUI dialog
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41   Parameters:
42       input=name [required]
43           Name of input vector map
44           Or data source for direct OGR access
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46       layer=string
47           Layer number or name (’-1’ for all layers)
48           A  single  vector map can be connected to multiple database tables.
49           This number determines which table to use. When  used  with  direct
50           OGR access this is the layer name.
51           Default: -1
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53       output=name [required]
54           Name for output vector map
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56       distribution=string
57           Distribution of perturbation
58           Options: uniform, normal
59           Default: uniform
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61       parameters=float[,float,...] [required]
62           Parameter(s) of distribution
63           If the distribution is uniform, only one parameter, the maximum, is
64           needed. For a normal distribution, two  parameters,  the  mean  and
65           standard deviation, are required.
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67       minimum=float
68           Minimum deviation in map units
69           Default: 0.0
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71       seed=integer
72           Seed for random number generation
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DESCRIPTION

75       v.perturb  reads  a vector map of points and writes the same points but
76       perturbs the eastings and northings by adding either a uniform or  nor‐
77       mal  delta value. Perturbation means that a variating spatial deviation
78       is added to the coordinates.
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NOTES

81       The uniform distribution is always centered about zero.  The associated
82       parameter  is  constrained  to be positive and specifies the maximum of
83       the distribution; the minimum is the negation  of  that  parameter.  Do
84       perturb  into  a  ring  around the center, the minimum parameter can be
85       used.
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87       Usually, the mean (first parameter) of the normal distribution is  zero
88       (i.e.,  the  distribution  is centered at zero). The standard deviation
89       (second parameter) is naturally constrained to be positive.
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91       Output vector points are not guaranteed to be contained within the cur‐
92       rent geographic region.
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EXAMPLES

95   Random, uniformly distributed selection
96       To  create  a  random,  uniformly distributed selection of possible new
97       points with a radius of 100,000 map units, use the following command:
98       v.perturb input=comm_colleges output=uniform_perturb parameters=100000
99       Your map should look similar to this figure:
100       Figure: Map showing the actual community college points  and  uniformly
101       random chosen points.
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103   Normal distributed selection
104       For a normal distribution with a mean of 5000 and standard deviation of
105       2000, use the following command:
106       v.perturb input=comm_colleges output=normal_perturb distribution=normal parameters=5000,2000
107       Figure: Map showing the actual community college  points  and  normally
108       random  chosen  and colored points. Notice that each point is closer to
109       the original point.
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111   Normal distributed selection with a minimum value
112       In order to include a minimum value of 500, use the following command:
113       v.perturb input=comm_colleges output=min_perturb distribution=normal parameters=100000,1000 minimum=500
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SEE ALSO

116        v.random, v.univar
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AUTHORS

119       James Darrell McCauley
120       when he was at: Agricultural Engineering Purdue University
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122       Random number generators originally written in FORTRAN by Wes  Peterson
123       and translated to C using f2c.
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SOURCE CODE

126       Available at: v.perturb source code (history)
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128       Accessed: Saturday Jan 21 21:16:17 2023
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130       Main  index  | Vector index | Topics index | Keywords index | Graphical
131       index | Full index
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133       © 2003-2023 GRASS Development Team, GRASS GIS 8.2.1 Reference Manual
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137GRASS 8.2.1                                                       v.perturb(1)