[GRASS-SVN] r54808 - grass/branches/develbranch_6/vector/v.net.distance

[svn_grass at osgeo.org]

Author: mlennert
Date: 2013-01-28 02:22:39 -0800 (Mon, 28 Jan 2013)
New Revision: 54808

Modified:
   grass/branches/develbranch_6/vector/v.net.distance/description.html
Log:
Added note indicating that from and to nodes should be different (#1861)


Modified: grass/branches/develbranch_6/vector/v.net.distance/description.html
===================================================================
--- grass/branches/develbranch_6/vector/v.net.distance/description.html	2013-01-28 10:19:57 UTC (rev 54807)
+++ grass/branches/develbranch_6/vector/v.net.distance/description.html	2013-01-28 10:22:39 UTC (rev 54808)
@@ -23,6 +23,15 @@
 The costs of arcs in forward and backward direction are specified by 
 <b>afcolumn</b> and <b>abcolumn</b> columns respectively. If 
 <b>abcolumn</b> is not given, the same cost is used in both directions.  
+<p>
+<em>v.net.distance</em> will not work if you are trying to find the nearest
+neighbors within a group of nodes, i.e. where <em>to</em> and <em>from</em>
+are the same set of nodes, as the closest node will be the node itself and
+the result will be zero-length paths. In order to find nearest neighbors
+within a group of nodes, you can either loop through each node as <em>to</em>
+and all other nodes as <em>from</em> or create a complete distance matrix with
+<a href="v.net.allpairs.html">v.net.allpairs</a> and select the lowest non-zero
+distance for each node.
 
 <h2>EXAMPLES</h2>
 Find shortest path and distance from every school to the nearest hospital