[GRASS-SVN] r43979 - grass/trunk/vector/v.build.polylines

[svn_grass at osgeo.org]

Author: martinl
Date: 2010-10-20 04:08:29 -0700 (Wed, 20 Oct 2010)
New Revision: 43979

Modified:
   grass/trunk/vector/v.build.polylines/v.build.polylines.html
Log:
v.build.polylines: manual page updated (notes my Markus Metz, http://lists.osgeo.org/pipermail/grass-user/2010-October/058400.html)


Modified: grass/trunk/vector/v.build.polylines/v.build.polylines.html
===================================================================
--- grass/trunk/vector/v.build.polylines/v.build.polylines.html	2010-10-19 23:30:29 UTC (rev 43978)
+++ grass/trunk/vector/v.build.polylines/v.build.polylines.html	2010-10-20 11:08:29 UTC (rev 43979)
@@ -1,15 +1,32 @@
 <h2>DESCRIPTION</h2>
 
 <em>v.build.polylines</em> builds polylines from the lines or
-boundaries in a vector map.  <!-- ???? and copies the attribute
-and category files from the original file. -->
-<P>
+boundaries in a vector map.
+
+<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>
+
+<p>
+<em>v.build.polyline</em> picks a line and from its start node, walks
+back as long as exactly one other line is connected to this node. Line
+directions are reversed as required, i.e. it does not matter if the
+next line is connected to the current node by its start or end
+node. Once the start line of a polyline is identified, it walks
+forward and adds all vertices (in reverse order if needed) of
+connected lines to the start line, i.e. the start line and connecting
+lines are reversed as needed. That is, if a line is reversed depends
+on what node is initially picked for building polylines. If the
+direction of lines is important (it's not for boundaries to build
+areas), you have to manually change line directions with
+either <em><a href="v.edit.html">v.edit</a></em> or
+the <em><a href="wxGUI.Vector_Digitizing_Tool.html">wxGUI vector
+digitizer</a></em>.
+
+<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 
@@ -18,52 +35,49 @@
 polylines. 
 
 <h2>NOTES</h2>
-<p>
 
 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. 
--->
+<em>v.build.polylines</em> will set the type from the first constituent line.  
+
 <p>
-
 Category number(s) are assigned to a polyline based on <b>cats</b> parameter.
 
 <ul>
-  <li>cats=no - No category number is assigned to a polyline. Also
-  attributes tables linked to the input vector map are not copied to
-  the output vector map.</li>
-  <li>cats=first - Assign to a polyline category number of the first
-line. All linked attributes tables are copied to the output vector map.</li>
-  <li>cats=multi - If the lines that make up a polyline have different category numbers
-    then <em>v.build.polylines</em> will set the multiple catetory numbers to a polyline.
-    Also all linked attributes tables are copied to the output vector map.</li>
+  <li><b>cats=no</b> - No category number is assigned to a
+  polyline. Also attributes tables linked to the input vector map are
+  not copied to the output vector map.</li>
+  <li><b>cats=first</b> - Assign to a polyline category number of the
+first line. All linked attributes tables are copied to the output
+vector map.</li>
+  <li><b>cats=multi</b> - If the lines that make up a polyline have
+    different category numbers then <em>v.build.polylines</em> will
+    set the multiple catetory numbers to a polyline.  Also all linked
+    attributes tables are copied to the output vector map.</li>
 </ul>
 
-<p>
 <em>v.build.polylines</em> correctly handles <b>input</b> vector maps
 containing lines, boundaries, centroids and points. Lines and
 boundaries 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 boundaries in the input vector 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??] -->
+<!-- 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>
 
-<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> 
+
 <em>
-<a href=v.build.html>v.build</a>,
-<a href=v.in.ascii.html>v.in.ascii</a>,
-<a href="v.split.html">v.split</a>,
-<a href="v.edit.html">v.edit</a>
+  <a href="v.build.html">v.build</a>,
+  <a href="v.in.ascii.html">v.in.ascii</a>,
+  <a href="v.split.html">v.split</a>,
+  <a href="v.edit.html">v.edit</a>
 </em>
 
 <h2>AUTHORS</h2>
@@ -71,4 +85,5 @@
 Major rewrite by Radim Blazek, October 2002<br>
 Category mode added by Martin Landa, FBK-irst, Trento, Italy, October 2007
 
-<p><i>Last changed: $Date$</i>
+<p>
+<i>Last changed: $Date$</i>