r.to.vect manual: examples added

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@58592 15284696-431f-4ddb-bdfa-cd5b030d7da7

raster/r.to.vect/r.to.vect.html

@@ -4,12 +4,12 @@
 layer, extracts points, lines or area edge features from it, converts data
 to GRASS vector format.
 
-<h3>Points</h3>
+<h3>Point conversion</h3>
 
-The <em>r.to.vect</em> program extracts data from a GRASS raster map layer and stores output 
-in a new GRASS <em>vector</em> file.  
+The <em>r.to.vect</em> program extracts data from a GRASS raster map 
+layer and stores output in a new GRASS <em>vector</em> file.  
 
-<h3>Lines</h3>
+<h3>Line conversion</h3>
 <em>r.to.vect</em> assumes that the <em>input</em> map has been thinned
 using <em><a href="r.thin.html">r.thin</a></em>.
 
@@ -28,7 +28,7 @@ These excessive nodes and spurs may be removed using
 <em><a href="v.clean.html">v.clean</a></em>.
 
 
-<h3>Areas</h3>
+<h3>Area conversion</h3>
 
 <em>r.to.vect</em> first traces the perimeter of each unique
 area in the raster map layer and creates vector data to
@@ -39,7 +39,7 @@ resultant vector area edge data.
 <p>
 A true vector tracing of the area edges might appear
 blocky, since the vectors outline the edges of raster data
-that are stored in rectangular cells.  To produce a
+that are stored in rectangular cells. To produce a
 better-looking vector map, <em>r.to.vect</em> smoothes the
 corners of the vector data as they are being extracted. At
 each change in direction (i.e., each corner), the two
@@ -54,9 +54,53 @@ region (and the original data) to estimate the possible
 error introduced by smoothing.
 
 <p>
-<em>r.to.vect</em> extracts only area edges from the named raster input file. 
-If the raster map contains other data (i.e., line edges, or point data) the
-output may be wrong. 
+<em>r.to.vect</em> extracts only area edges from the named raster 
+input file. If the raster map contains other data (i.e., line edges, 
+or point data) the output may be wrong.
+
+<h2>EXAMPLES</h2>
+
+The examples are based on the North Carolina sample dataset:
+<p>
+<b>Conversion of raster points to vector points:</b>
+<p>
+Random sampling of points:
+<div class="code"><pre>
+g.region rast=elevation -p
+# random sampling of points (note that r.random also writes vector points)
+r.random elevation raster_output=elevrand1000 n=1000
+r.to.vect input=elevrand1000 output=elevrand1000 type=point
+# univariate statistics of sample points
+v.univar elevrand1000 column=value type=point
+# compare to univariate statistics on original full raster map
+r.univar elevation
+</pre></div>
+<p>
+
+<b>Conversion of raster lines to vector lines:</b>
+<p>
+Vectorization of streams in watershed basins map:
+<div class="code"><pre>
+g.region rast=elevation -p
+r.watershed elev=elevation stream=elev.streams thresh=50000
+r.to.vect -s input=elev.streams output=elev_streams type=line
+# drop "label" column which is superfluous in this example
+v.db.dropcolumn map=elev_streams column=label
+v.db.renamecolumn map=elev_streams column=value,basin_id
+# report length per basin ID
+v.report map=elev_streams option=length units=meters sort=asc
+</pre></div>
+<p>
+
+<b>Conversion of raster polygons to vector polygons:</b>
+<p>
+Vectorization of simplified landuse class map:
+<div class="code"><pre>
+g.region rast=landclass96 -p
+# we smooth corners of area features
+r.to.vect -s input=landclass96 output=my_landclass96 type=area
+v.colors my_landclass96 color=random
+</pre></div>
 
 <h2>BUGS</h2>
 
@@ -64,19 +108,27 @@ For type=line the input raster map MUST be thinned by
 <em><a href="r.thin.html">r.thin</a></em>;
 if not, <em>r.to.vect</em> may crash.
 
-<h2>AUTHOR</h2>
-<b>Points</b><br>
+<h2>SEE ALSO</h2>
+
+<em>
+<a href="g.region.html">g.region</a>,
+<a href="r.thin.html">r.thin</a>,
+<a href="v.clean.html">v.clean</a>
+</em>
+
+<h2>AUTHORS</h2>
+<b>Point support</b><br>
 Bill Brown<br>
 <br>
 
-<b>Lines</b><br>
+<b>Line support</b><br>
 Mike Baba<br>
 DBA Systems, Inc.<br>
 10560 Arrowhead Drive<br>
 Fairfax, Virginia 22030<br>
 <br>
 
-<b>Areas</b><br>
+<b>Area support</b><br>
 <em>Original</em> version of <em>r.poly</em>: 
 <br>
 Jean Ezell and Andrew Heekin,