Geografic-Information-System/vector/v.random/v.random.html

<h2>DESCRIPTION</h2>

<em>v.random</em> randomly generates vector points within the
current region using the selected random number generator.

<p><em>v.random</em> can generate also 3D vector points or
write random value to attribute table. Point height range or
attribute value range is controlled by specifying zmin and zmax values.
Both z values are included in range (<em>zmin &lt;= z &lt;= zmax</em>).
Generated random attribute value type can be controlled by column
data type. Use <b>INTEGER</b> column type for integers and 
<b>DOUBLE PRECISION</b> for floating point numbers. Integer values are
calculated by rounding random floating point number.

<p>To produce repeatable results a random seed can be set using the
option <em>seed</em>.

<h3>Restriction to vector areas</h3>
<p>
If an <em>input</em> vector map with areas is specified, the location of 
random points is restricted to the selected areas. By default, the 
requested number of points are distributed across all areas.

<p>
If the <em>-a</em> flag is given, the requested number of points is 
generated for each individual area. For example, if 20 points should be 
generated and the input map has 100 individual areas, 2000 points will 
be generated in total.

<h2>EXAMPLES</h2>
All examples use the North Carolina sample dataset.
<p>
Generate 20 random points with binary attribute (only 0 or 1):
<div class="code"><pre>
v.random output=binary_random npoints=20 zmin=0 zmax=1 column='binary INTEGER'
</pre></div>

Generate 20 random 3D points using a specific random seed:
<div class="code"><pre>
v.random seed=52 output=height_random npoints=40 zmin=110 zmax=170 -z
</pre></div>

<p>
<center>
<img src="vrandom_z.png"><br>
Random points with different X, Y, and Z coordinates
</center>

<!--
g.region rast=elev_lid792_1m
...
d.vect height_random color=60:60:60 icon=basic/point size=40 width=2 zcolor=gyr
optipng -o5 map.png
mv map.png vrandom_z.png
-->

Get 20 random samples from raster map:
<div class="code"><pre>
g.region -p raster=elevation
v.random output=random_samples npoints=20
v.db.addtable map=random_samples layer=1 columns='cat INTEGER, sample DOUBLE PRECISION'
v.what.rast vector=random_samples raster=elevation@PERMANENT layer=1 column=sample 
</pre></div>

Generate 20 random points and sample attribute data from geology (vector) map:
<div class="code"><pre>
g.region -p vector=geology
v.random output=random_samples npoints=20
v.db.addtable map=random_samples layer=1 columns='cat integer, geology varchar(100)'
v.what.vect vector=random_samples layer=1 column=geology \
  qvector=geology@PERMANENT qlayer=1 qcolumn=label 
</pre></div>

Generate 20 random points in forested areas
<div class="code"><pre>
g.region -p raster=landclass96
r.to.vect -v input=landclass96 output=landclass96 type=area
v.random input=landclass96 output=random_samples npoints=20 \
  where="label = 'forest'"
</pre></div>

Generate 20 random points in each forest patch
<div class="code"><pre>
g.region -p raster=landclass96
r.to.vect -v input=landclass96 output=landclass96 type=area
v.random input=landclass96 output=random_samples npoints=20 \
  where="label = 'forest'" -a
</pre></div>


<h2>SEE ALSO</h2>

<em>
<a href="g.region.html">g.region</a>,
<a href="r.random.html">r.random</a>,
<a href="v.perturb.html">v.perturb</a>,
<a href="v.sample.html">v.sample</a>,
<a href="v.what.rast.html">v.what.rast</a>,
<a href="v.what.vect.html">v.what.vect</a>
</em>

<h2>AUTHOR</h2>

<a href="http://mccauley-usa.com/">James Darrell McCauley</a>
<a href="mailto:darrell@mccauley-usa.com">&lt;darrell@mccauley-usa.com&gt;</a>,
<br>when he was at: 
<a href="http://ABE.www.ecn.purdue.edu/ABE/">Agricultural
Engineering</a>
<a href="http://www.purdue.edu/">Purdue University</a>

<p><i>Last changed: $Date$</i>