1r.random(1)                 GRASS GIS User's Manual                r.random(1)
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NAME

6       r.random   - Creates a raster map layer and vector point map containing
7       randomly located points.
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KEYWORDS

10       raster, sampling, vector, random, level1
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SYNOPSIS

13       r.random
14       r.random --help
15       r.random   [-zidb]    input=name     [cover=name]     npoints=number[%]
16       [raster=name]      [vector=name]      [seed=integer]      [--overwrite]
17       [--help]  [--verbose]  [--quiet]  [--ui]
18
19   Flags:
20       -z
21           Generate points also for NULL category
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23       -i
24           Report information about input raster and exit
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26       -d
27           Generate vector points as 3D points
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29       -b
30           Do not build topology
31           Do not build topology in points mode
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33       --overwrite
34           Allow output files to overwrite existing files
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36       --help
37           Print usage summary
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39       --verbose
40           Verbose module output
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42       --quiet
43           Quiet module output
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45       --ui
46           Force launching GUI dialog
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48   Parameters:
49       input=name [required]
50           Name of input raster map
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52       cover=name
53           Name of cover raster map
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55       npoints=number[%] [required]
56           The number of points to allocate
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58       raster=name
59           Name for output raster map
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61       vector=name
62           Name for output vector map
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64       seed=integer
65           Seed for rand() function
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DESCRIPTION

68       The program r.random allows the user  to  create  a  raster  map  layer
69       and/or a vector points map containing coordinates of points whose loca‐
70       tions have been randomly determined.  The program  locates  these  ran‐
71       domly  generated  vector  points  (sites) within the current geographic
72       region and mask (if any), on non-NULL category value data areas  within
73       a user-specified raster map layer. If the user sets the -z flag, points
74       will be randomly generated across all cells (even those with NULL  val‐
75       ues).
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77       The category values and corresponding category names already associated
78       with the random point locations in the input map layer are assigned  to
79       these  points  in  the raster_output map layer. If the -z is specified,
80       then a unique entry is made for the value  used  where  the  input  was
81       NULL.   This  value  is  at least 1 less than the smallest value in the
82       input raster and is given a medium gray color.
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NOTES

85       If a cover raster map is specified and the cover map contains NULL  (no
86       data)  values, these points are suppressed in the resulting vector_out‐
87       put or raster_output map.
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89       The vector_output file created by r.random contains vector points  that
90       represent  the  center points of the randomly generated cells.  A value
91       attribute contains the cell value of the input raster (or the  assigned
92       value when -z is used).
93       If  a  cover map is additionally specified, a second column  covervalue
94       is populated with raster values from the cover map.
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96       If the user sets the -b flag, vector points are written without  topol‐
97       ogy  to  minimize  the  required  resources.  This is suitable input to
98       v.surf.rst and other vector modules.
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100       The user may specify the quantity of random locations to  be  generated
101       either  as  a  positive  integer  (e.g., 10), or as a percentage of the
102       raster map layer’s cells (e.g., 10%, or 3.05%).  The  number  of  cells
103       considered  for  the percentage reflects whether or not the -z flag was
104       given. Options are 0-100; percentages less  than  one  percent  may  be
105       stated as decimals.
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107       Flag  -i prints the raster map’s name and location, the total number of
108       cells under the current region settings, and the number of NULL  valued
109       cells  under  the  current  region settings.  Then module exits without
110       doing anything.  Useful for deciding on the number  of  sites  to  have
111       r.random  create.   WARNING: this feature may be removed in future. Use
112       g.region and r.report instead.
113       g.region -p
114       r.report map=inputmap units=c null=* nsteps=1
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116       To create random vector point  locations  within  some,  but  not  all,
117       non-zero  categories of the input raster map layer, the user must first
118       create a reclassified raster map layer of the original raster map layer
119       (e.g.,  using  the  GRASS  program  r.reclass)  that  contains only the
120       desired categories, and then use the  reclassed  raster  map  layer  as
121       input to r.random.
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EXAMPLES

124       Random  vector  elevation  points  sampled  from  elevation  map in the
125       Spearfish region, result stored in 2D vector map:
126       g.region raster=elevation.10m -p
127       r.random elevation.10m vector=elevrand n=100
128       v.db.select elevrand
129       v.univar elevrand col=value type=point
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131       Random vector elevation  points  sampled  from  elevation  map  in  the
132       Spearfish  region  with  collocated  values  sampled  from landuse map,
133       result stored in 3D vector map:
134       g.region raster=elevation.10m -p
135       r.random -d elevation.10m cover=landcover.30m vector=luserand3d n=100
136       # data output (value: elevation, covervalue: landuse class):
137       v.db.select luserand3d
138       cat|value|covervalue
139       1|1151.406616|81
140       2|1172.121216|71
141       3|1183.219604|71
142       ...
143

KNOWN ISSUES

145       It’s not possible to use the -i flag and not also specify the n parame‐
146       ter.
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SEE ALSO

149        g.region
150       r.reclass
151       v.random
152       v.surf.rst
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AUTHOR

155       Dr. James Hinthorne, GIS Laboratory, Central Washington University
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157       Modified for GRASS 5.0 by Eric G. Miller
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159       Cover map support by Markus Neteler, 2007
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SOURCE CODE

162       Available at: r.random source code (history)
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164       Main  index  | Raster index | Topics index | Keywords index | Graphical
165       index | Full index
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167       © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
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171GRASS 7.8.5                                                        r.random(1)
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