https://grasswiki.osgeo.org/w/index.php?action=history&feed=atom&title=Streams_extraction_from_streams_map 2026-04-13T20:54:51Z Revision history for this page on the wiki MediaWiki 1.41.0 https://grasswiki.osgeo.org/w/index.php?title=Streams_extraction_from_streams_map&diff=9013&oldid=prev 2009-06-05T20:36:08Z

<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 &quot;602042|4927928&quot; | 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>

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