r.randomgrass - Online in the Cloud

PROGRAM:

NAME

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

KEYWORDS

raster, sampling, vector, random

SYNOPSIS

r.random
r.random --help
r.random [-zidb] input=name [cover=name] npoints=number[%] [raster=name]
[vector=name] [--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 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

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.

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