Geografic-Information-System/scripts/v.colors/v.colors.html

<H2>DESCRIPTION</H2>

<EM>v.colors</EM> is much like <em>r.colors</em>, but may be used for vector maps.
You give it a vector map and numeric data column, together with color rules
like you would do for a raster. It creates a new column in the database with
R:G:B values suitable for use with '<tt>d.vect -a</tt>'.

<P>
How it works: it creates a dummy raster map with the same data range as
the vector's column then runs <em>r.colors</em> for that temporary map.
It then uses <em>r.what.colors</em> for each value found by <em>v.db.select</em>
and uploads it a new column in the vector map's attribute database.

<P>
It is planned that this script will be replaced with a C display module which
renders thematic vector maps directly instead requiring the overhead of
saving the colors into the DB.

<P>
If the target column name given by the <b>rgb_column</b> option does
not exist, it will be created. The default name is "<tt>GRASSRGB</tt>".

<h2>EXAMPLES</h2>

Create a random sample point map, query raster map values for those points,
and colorize output.

<div class="code"><pre>
# Spearfish dataset
g.region -d
v.random out=rand5k_elev n=5000
v.db.addtable map=rand5k_elev column='elevation double precision'
v.what.rast vector=rand5k_elev raster=elevation.10m column=elevation
v.colors map=rand5k_elev column=elevation color=bcyr

# display colorized points map
d.mon x0
d.vect -a rand5k_elev
</pre></div>

<p>
Colorizing the roads map in Spearfish:
<div class="code"><pre>
g.copy vect=roads,myroads
echo "1 red
2 yellow
3 orange
4 black
5 grey" &gt; colors.txt

v.colors myroads column=cat rules=colors.txt

# display colorized roads map
d.mon x0
d.vect -a myroads
</pre></div>


<P>
Colorizing a TIN (polygons) generated by <em>v.delaunay</em>:

<div class="code"><pre>
# new columns for x,y,z of centroids
v.db.addtable map=tin \
   columns="east double precision, north double precision, height double precision, GRASSRGB varchar(11)"

# transfer geometry for colorizing (we need the centroid height)
v.to.db tin option=coor columns="east,north,height"
v.db.select tin

v.colors tin column=height rgb_column=GRASSRGB color=rainbow

# display colorized triangles
d.mon x0
d.vect -a tin
</pre></div>


<H2>SEE ALSO</H2>

<EM>
<A HREF="d.vect.html">d.vect</a> -z<br>
<A HREF="r.colors.html">r.colors</A><BR>
<A HREF="r.colors.stddev.html">r.colors.stddev</A><BR>
<A HREF="r.what.color.html">r.what.color</A><BR>
<A HREF="v.db.addcolumn">v.db.addcolumn</A><BR>
<A HREF="v.db.select.html">v.db.select</A><BR>
<A HREF="db.execute.html">db.execute</A>
</EM>



<H2>AUTHOR</H2>

Hamish Bowman<BR>
<i>Dunedin, New Zealand</i>

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