https://grasswiki.osgeo.org/w/index.php?title=Streams_extraction_from_streams_map&feed=atom&action=historyStreams extraction from streams map - Revision history2024-03-28T19:26:26ZRevision history for this page on the wikiMediaWiki 1.41.0https://grasswiki.osgeo.org/w/index.php?title=Streams_extraction_from_streams_map&diff=9013&oldid=prevNeteler: new2009-06-05T20:36:08Z<p>new</p>
<p><b>New page</b></p><div>'''Q:''' I have a network of streams (say, Spearfish or better the new NC data set at http://www.grassbook.org/data_menu3rd.php ) and want to extract a single stream system. Names are lacking, is there any trick to extract topologically connected lines into a new map? <br />
<br />
'''A:''' Use {{cmd|v.net.iso}} since disconnected networks will have infinite cost.<br />
<br />
Spearfish example: <br />
<br />
g.region vect=streams<br />
d.mon 0<br />
d.vect streams disp=shape,dir<br />
<br />
# find coordinates<br />
d.where<br />
<br />
# work on map copy<br />
g.copy vect=streams,mystreams<br />
<br />
echo "602042|4927928" | v.in.ascii out=outlet --o<br />
v.distance -p from=outlet to=mystreams out=connect upload=dist column=dist --o<br />
<br />
v.patch in=mystreams,connect,outlet out=streams_n --o<br />
v.clean streams_n out=streams_net tool=snap,break thresh=5,0 --o<br />
<br />
g.region vect=streams_net<br />
d.erase<br />
d.vect streams_net<br />
d.vect streams_net type=point col=red icon=basic/triangle<br />
<br />
v.net.iso streams_net out=myriver ccats=1 costs=99999999 nlayer=1 --o<br />
<br />
v.category myriver option=report<br />
# The network is of 2 categories<br />
# show selected river network<br />
d.vect myriver col=blue cats=1<br />
d.vect myriver col=green cats=2<br />
<br />
# now v.extract etc ...<br />
<br />
Note that some upper parts of the river network are not found due to unconnected lines.<br />
<br />
[[Category: FAQ]]</div>Neteler