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

Provided by: grass-doc_7.8.2-1build3_all

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.

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

SOURCE CODE

       Available at: r.random source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual