[GRASS-SVN] r73787 - grass/branches/releasebranch_7_6/vector/v.split
svn_grass at osgeo.org
svn_grass at osgeo.org
Mon Dec 10 11:21:47 PST 2018
Author: neteler
Date: 2018-12-10 11:21:47 -0800 (Mon, 10 Dec 2018)
New Revision: 73787
Modified:
grass/branches/releasebranch_7_6/vector/v.split/v.split.html
Log:
v.split manual: added segment length notes (contributed by M. Lennert and Ken Mankoff; sync to trunk)
Modified: grass/branches/releasebranch_7_6/vector/v.split/v.split.html
===================================================================
--- grass/branches/releasebranch_7_6/vector/v.split/v.split.html 2018-12-10 19:20:51 UTC (rev 73786)
+++ grass/branches/releasebranch_7_6/vector/v.split/v.split.html 2018-12-10 19:21:47 UTC (rev 73787)
@@ -5,6 +5,48 @@
is expected to be equal and not higher than the given <b>length</b>
parameter.
+<h2>NOTES</h2>
+
+<em>v.split</em> does not change the layer, nor the category information,
+nor the attribute table links of the original file. It just splits each
+line in segments and attributes the same category to all segments of the same
+original line. As the attribute table is linked to the features with
+their category as key, all segments originating from the same original
+line are linked to the same line in the original attribute table which
+is just copied to the new map.
+
+<h3>Notes on individual segment information</h3>
+
+When running <em>v.to.db</em> on a map produced by <em>v.split</em>,
+<em>v.to.db</em> will add length information for each segment in its
+respective attribute line, but since all the segments of the same
+original line share the same attribute table line, it only gets
+updated once.
+
+<p>
+To obtain the length of each segment, the user will have to attribute
+different category values to each of them. The best way to do this on
+a separate layer, using <em>v.category</em>
+
+<div class="code"><pre>
+v.category v_split op=add layer=2 output=v_split_2
+</pre></div>
+
+and then run the following commands on the new layer 2:
+
+<div class="code"><pre>
+v.db.addtable v_split_2 layer=2
+v.db.addcolumn map=v_split_2 column="length double precision" layer=2
+v.to.db map=v_split_2 type=line option=length columns=length units=meters layer=2
+</pre></div>
+
+To link the new segments in the new layer to the original segments, use:
+
+<div class="code"><pre>
+v.db.addcolumn map=v_split_2 layer=2 column="cat_1 int"
+v.to.db map=v_split_2 layer=2 option=query query_layer=1 query_column=cat columns=cat_1
+</pre></div>
+
<h2>EXAMPLES</h2>
The examples are based on the North Carolina sample data location.
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