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NAME

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

KEYWORDS

       raster, sampling, vector, random, level1

SYNOPSIS

       r.random
       r.random --help
       r.random    [-zidb]    input=name     [cover=name]     npoints=number[%]     [raster=name]
       [vector=name]   [seed=integer]   [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       -z
           Generate points also for NULL category

       -i
           Report information about input raster and exit

       -d
           Generate vector points as 3D points

       -b
           Do not build topology
           Do not build topology in points mode

       --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

   Parameters:
       input=name [required]
           Name of input raster map

       cover=name
           Name of cover raster map

       npoints=number[%] [required]
           The number of points to allocate

       raster=name
           Name for output raster map

       vector=name
           Name for output vector map

       seed=integer
           Seed for rand() function

DESCRIPTION

       The  program  r.random allows the user to create a raster map layer and/or a vector points
       map containing coordinates of points whose locations have been randomly  determined.   The
       program  locates  these  randomly  generated  vector  points  (sites)  within  the current
       geographic region and mask (if any), on  non-NULL  category  value  data  areas  within  a
       user-specified  raster  map  layer.  If the user sets the -z flag, points will be randomly
       generated across all cells (even those with NULL values).

       The category values and corresponding category names already associated  with  the  random
       point  locations  in the input map layer are assigned to these points in the raster_output
       map layer. If the -z is specified, then a unique entry is made for the  value  used  where
       the  input  was  NULL.  This value is at least 1 less than the smallest value in the input
       raster and is given a medium gray color.

NOTES

       If a cover raster map is specified and the cover map contains NULL (no data) values, these
       points are suppressed in the resulting vector_output or raster_output map.

       The  vector_output  file  created  by  r.random  contains vector points that represent the
       center points of the randomly generated cells.  A value attribute contains the cell  value
       of the input raster (or the assigned value when -z is used).
       If  a  cover  map is additionally specified, a second column  covervalue is populated with
       raster values from the cover map.

       If the user sets the -b flag, vector points are written without topology to  minimize  the
       required resources. This is suitable input to v.surf.rst and other vector modules.

       The user may specify the quantity of random locations to be generated either as a positive
       integer (e.g., 10), or as a percentage of the raster map  layer’s  cells  (e.g.,  10%,  or
       3.05%).   The number of cells considered for the percentage reflects whether or not the -z
       flag was given. Options are 0-100; percentages less than one  percent  may  be  stated  as
       decimals.

       Flag  -i  prints  the  raster map’s name and location, the total number of cells under the
       current region settings, and the number of NULL valued  cells  under  the  current  region
       settings.  Then module exits without doing anything.  Useful for deciding on the number of
       sites to have r.random create.  WARNING: this  feature  may  be  removed  in  future.  Use
       g.region and r.report instead.
       g.region -p
       r.report map=inputmap units=c null=* nsteps=1

       To  create  random vector point locations within some, but not all, non-zero categories of
       the input raster map layer, the user must first create a reclassified raster map layer  of
       the original raster map layer (e.g., using the GRASS program r.reclass) that contains only
       the desired categories, and then use the reclassed raster map layer as input to r.random.

EXAMPLES

       Random vector elevation points sampled from elevation map in the Spearfish region,  result
       stored in 2D vector map:
       g.region raster=elevation.10m -p
       r.random elevation.10m vector=elevrand n=100
       v.db.select elevrand
       v.univar elevrand col=value type=point

       Random  vector  elevation  points  sampled from elevation map in the Spearfish region with
       collocated values sampled from landuse map, result stored in 3D vector map:
       g.region raster=elevation.10m -p
       r.random -d elevation.10m cover=landcover.30m vector=luserand3d n=100
       # data output (value: elevation, covervalue: landuse class):
       v.db.select luserand3d
       cat|value|covervalue
       1|1151.406616|81
       2|1172.121216|71
       3|1183.219604|71
       ...

KNOWN ISSUES

       It’s not possible to use the -i flag and not also specify the n parameter.

SEE ALSO

        g.region
       r.reclass
       v.random
       v.surf.rst

AUTHOR

       Dr. James Hinthorne, GIS Laboratory, Central Washington University

       Modified for GRASS 5.0 by Eric G. Miller

       Cover map support by Markus Neteler, 2007

       Last changed: $Date: 2015-05-11 02:11:34 +0200 (Mon, 11 May 2015) $

SOURCE CODE

       Available at: r.random source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.6.0 Reference Manual