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<h2>DESCRIPTION</h2>
<em>v.build.polylines</em> builds polylines from the lines in a binary vector file.
<!-- ???? and copies the attribute and category files from the original file. -->
<P>
A line is a single straight line segment defined by one start node, one end
node and no other nodes. A polyline is also defined by one start node, one end
node and no other nodes, but is made of two or more consecutive straight line
segments. The connections between the constituent line segments of a polyline
do not appear as nodes in the vector map.
<P>
Polylines provide the most appropriate representation of curved lines when it
is important that nodes serve to define topology rather than geometry. Curved
lines are usually digitized as polylines, but these are sometimes broken into
their constituent straight line segments during conversion from one data
format to another. <em>v.build.polylines</em> can be used to rebuild such broken
polylines.
<h2>NOTES</h2>
<p>
<!-- begin untrue?? -->
If the lines that make up a polyline are of different types, then
<i>v.build.polylines</i> will set the type from the first constituent line.
<i>v.build.polylines </i> will issue a warning unless the flag <b>-q</b> has
been set. It is possible to keep a list of all such warnings by redirecting
standard output to a file.
<!-- end untrue ??-->
<p>
If the lines that make up a polyline have different attribute values
then <i>v.build.polylines</i> will set the attribute value of the polyline to
that of the last line <!-- still true?? --> (this is the behaviour of
<i>v.build</i>, which is used to assign the attribute values). <!-- untrue?? -->
<p>
<i>v.build.polylines</i> correctly
handles <b>input</b> maps containing lines, area edges and points. Lines and
area edges will be converted to polylines of the desired type. Areas
are only guaranteed to be preserved if the constituent lines of the polylines
that define them are all area edges in the input map.
<!-- Points will remain points provided that <b>type</b> has been set to `source'.
It is possible to convert lines and area edges to points or vice versa, but this
is rarely useful. [type no longer exists, other behaviour still true??] -->
<h2>ACKNOWLEDGEMENTS</h2>
This program was originally written during Mark Lake's tenure of a
Leverhulme Special Research Fellowship at University College London.
<h2>SEE ALSO</h2>
<i><a href=v.build.html>v.build</a></i><br>
<i><a href=v.in.ascii.html>v.in.ascii</a></i><br>
<i><a href=parser.html>parser</a></i> <p>
<h2>AUTHORS</h2>
Mark Lake, Institute of Archaeology, University College London.
Major rewrite by Radim Blazek, October 2002
<p><i>Last changed: $Date: 2004/07/22 12:13:17 $</i>
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