Geografic-Information-System/raster/r.to.vect/r.to.vect.html

<h2>DESCRIPTION</h2>

<em>r.to.vect</em> scans the named <b>input</b> raster map
layer, extracts points, lines or area edge features from it, converts data
to GRASS vector format.

<h3>Points</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.  

<h3>Lines</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>.

<p>
<em>r.to.vect</em> extracts vectors (aka, "arcs") from a
raster map.  These arcs may represent linear features
(like roads or streams), or may represent area edge
features (like political boundaries, or soil mapping
units).  

<p>
<em><a href="r.thin.html">r.thin</a></em> and <em>r.to.vect</em>
may create excessive nodes at every junction, and may create small spurs
or "dangling lines" during the thinning and vectorization process.
These excessive nodes and spurs may be removed using
<em><a href="v.clean.html">v.clean</a></em>.


<h3>Areas</h3>

<em>r.to.vect</em> first traces the perimeter of each unique
area in the raster map layer and creates vector data to
represent it.  The cell category values for the raster map
layer will be used to create attribute information for the
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
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
midpoints of the corner cell (half the cell's height and
width) are taken, and the line segment connecting them is
used to outline this corner in the resultant vector map.
(The cell's cornermost node is ignored.) Because vectors
are smoothed by this program, the resulting vector map will
not be "true" to the raster map from which it was created.
The user should check the resolution of the geographic
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. 

<h2>BUGS</h2>

For feature=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>
Bill Brown<br>
<br>

<b>Lines</b><br>
Mike Baba<br>
DBA Systems, Inc.<br>
10560 Arrowhead Drive<br>
Fairfax, Virginia 22030<br>
<br>

<b>Areas</b><br>
<em>Original</em> version of <em>r.poly</em>: 
<br>
Jean Ezell and Andrew Heekin, 
<br>
U.S. Army Construction Engineering 
Research Laboratory

<p><em>Modified</em> program for smoothed lines: 
<br>
David Satnik, 
Central Washington University
<br>
Updated 2001 by Andrea Aime, Modena, Italy<br>
<br>

<b>Update</b><br>
Original r.to.sites, r.line and r.poly merged and updated to 5.7 by Radim Blazek

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