On Thu, Mar 12, 2020 at 12:34 PM Johannes Radinger < johannesradin...@gmail.com> wrote: > > Thank you Markus, > indeed your approach looks like what I need..The hint with v.net.components was the part that I was missing;
Note that v.net.components does not need a network prepared with v.net, you can use the extract of all lines with the same stream order as it is. Markus M > I'll try as soon as possible and will report back on how this works. > cheers, > Johannes > > On Wed, Mar 11, 2020 at 10:16 PM Markus Metz < markus.metz.gisw...@gmail.com> wrote: >> >> Hi Johannes, >> >> IIUC, what you want to do is an operation that involves topological relations of vector geometries (connected lines) and a common attribute. There is no easy common recipe for this. >> >> Just a suggestion: >> for each stream order: >> extract all lines with this stream order (v.extract) >> identify connected lines (v.net + v.net.components) >> update a new attribute of the original lines with the comp attribute of the output of v.net.components plus some offset to separate different stream orders >> >> HTH, >> >> Markus M >> >> >> On Tue, Mar 10, 2020 at 5:20 PM Johannes Radinger < johannesradin...@gmail.com> wrote: >> > >> > So...no also with GRASS-user as recipient... >> > >> > On 05.03.20 16:21, Micha Silver wrote: >> > > >> > > On 3/5/20 10:47 AM, Johannes Radinger wrote: >> > >> >> > >> Hi Micha, hi all, >> > >> >> > >> sorry for my late response...however, just today I managed to try >> > >> your approach of building polylines to connect "touching stream >> > >> lines"...but... >> > >> >> > >> On 24.02.20 16:48, Micha Silver wrote: >> > >>> >> > >>> On 24/02/2020 10:45, Johannes Radinger wrote: >> > >>>> Hi all, >> > >>>> I have a large river network dataset (lines). Now I'd to assign >> > >>>> unique categories to each group of connected lines that have an >> > >>>> attribute in common. >> > >>>> >> > >>>> For example, my rivers are categorized based on some kind of stream >> > >>>> order. I want to group all rivers that belong to stream order 2 and >> > >>>> are spatially connected; each group should get a unique category >> > >>>> value. I thought that I could first extract all rivers with a >> > >>>> particular attribute (e.g. stream order = 2) which will provide me >> > >>>> some scattered pattern of lines. Then I need a spatial join tool to >> > >>>> make subgroups of lines that are connected. How can I achieve the >> > >>>> latter? Any idea? >> > >>> >> > > >> > > >> > >>> >> > >>> Here's a procedure that might work for you. Somewhat clunky, but I >> > >>> think it gets what you want. >> > >>> >> > >>> It's based on the v.build.polylines module to connect all touching >> > >>> stream reaches. First extract each order from the stream vector into >> > >>> a new vector. Then build polylines. Patch them all together. Now you >> > >>> have a polyline vector with a single cat value for each set of >> > >>> original stream reaches that had the same order and that were touching. >> > >> >> > >> Unfortunately, the v.build.polylines tool does not work as it only >> > >> does not connect multiple (intersecting) lines like in a river >> > >> network. As an example I tried to build polylines from the stream >> > >> network of the NC dataset. Yous suggested approach should result that >> > >> each sub-network (i.e. river network that is not connected to another >> > >> one) should get its own ID/cat...however, v.build.polylines results >> > >> in a connected stream network that consists of multiple cats: >> > >> >> > > Maybe I misunderstood your question. The steps I tried use a >> > > stream_order column to group stream segments, then apply a new >> > > attribute "merged_id" to those stream orders that touch. i.e. that >> > > connect to the same confluence point. >> > > >> > > >> > > Here's what I get using the nc_basic_spm mapset: >> > > >> > > >> > > r.watershed elev=elevation accum=nc_facc drain=nc_fdir bas=nc_bas >> > > stream=nc_str thresh=1000 >> > > r.stream.order stream_rast=nc_str direct=nc_fdir elev=elevation >> > > accum=nc_facc stream_vect=nc_streams >> > > ORDERS=`v.db.select -c nc_streams group=strahler column=strahler` >> > > echo $ORDERS >> > > >> > > # Create a new stream vector for each stream order >> > > >> > > for o in $ORDERS; do >> > > >> > > v.extract input=nc_streams output=streams_${o} where="strahler=${o}" >> > > >> > > # Give each polyline it's own cat value >> > > >> > > v.build.polylines input=streams_${o} output=streams_${o}_polyline >> > > type=line cat=first >> > > >> > > done >> > > >> > > >> > > # patch the stream orders back together >> > > >> > > POLYLINES=`g.list vect pattern="streams*polyline" separator=comma` >> > > >> > > v.patch input=$POLYLINES output=streams_polylines >> > > >> > > v.db.addcolumn map=streams column="merged_id INTEGER" >> > > >> > > >> > > # And use v.distance to update that merged_id column from cat values >> > > in polylines vector >> > > v.distance from=streams to=streams_polylines upload=cat column=merged_id >> > > v.db.addcolumn map=nc_streams column="merged_id INTEGER" >> > > v.distance from=nc_streams to=streams_polylines upload=cat >> > > column=merged_id >> > > >> > > Now, all stream reaches that have the same order and are "touching" >> > > have the same merged_id. See the attached image. >> > > >> > > >> > > If that's not your purpose, then just ignore... >> > > >> > Micha thank you for your help and of course, you're fully correct! >> > Merging lines that belong to the same stream order works in this case >> > well...but this is because of the definition of the Strahler ordering >> > system, where there is only one "touching node" (i.e. river junction) of >> > two rivers of the same stream order (i.e. when two 2nd order streams >> > meet, the become a 3rd order stream). Thus your solution works because >> > of this specifics and might not work if streams are grouped based on a >> > different (ordering) system. >> > >> > I was already thinking of the next step (beyond simple Strahler): As >> > mentioned in my initial post I am dealing with "some kind" of stream >> > order. It is similar to grouped stream orders (e.g. stream order 1-2 = >> > "headwater streams"). I tried to somehow reproduce my situation based on >> > your example of the NC dataset. What I basically did was to reassign a >> > new stream order "99" to all former 1st and 2nd order streams. Then I >> > did exactly what you did in your example, and of course I don't unique >> > merged_ids for the subnetworks of touching lines (see attached Figs) >> > that all belong the the same "order" 99 (the original strahler order 3 >> > works of course, see Fig.)...So is there a more general way (as said >> > something like v.dissolve but for lines/networks?): >> > >> > ##################### >> > g.region raster=elevation >> > >> > r.watershed --o elev=elevation accum=nc_facc drain=nc_fdir bas=nc_bas >> > stream=nc_str thresh=1000 >> > r.stream.order stream_rast=nc_str direct=nc_fdir elev=elevation >> > accum=nc_facc stream_vect=nc_streams >> > >> > #ORDERS=`v.db.select -c nc_streams group=strahler column=strahler` >> > #echo $ORDERS >> > >> > # Regroup orders 1-2 (to 99) >> > v.db.addcolumn map=nc_streams@test2 columns="strahler_groups INTEGER" >> > v.db.update map=nc_streams column=strahler_groups query_column=strahler >> > v.db.update map=nc_streams column=strahler_groups value=99 >> > where="strahler=1 OR strahler=2" >> > >> > NEWORDERS=`v.db.select -c nc_streams group=strahler_groups >> > column=strahler_groups` >> > echo $NEWORDERS >> > >> > # Create a new stream vector for each stream order >> > for o in $NEWORDERS; do >> > v.extract input=nc_streams output=streams_${o} >> > where="strahler_groups=${o}" >> > # Give each polyline it's own cat value >> > v.build.polylines input=streams_${o} output=streams_${o}_polyline >> > type=line cat=first >> > done >> > >> > d.vect -c map=streams_99_polyline@test2 >> > ################# >> > >> > Thank you very much! >> > >> > Cheers, >> > >> > Johannes >> > >> > > >> > >> v.clean --overwrite input=streams@PERMANENT output=streams_break >> > >> tool=break >> > >> v.build.polylines --overwrite input=streams_break@test >> > >> output=streams_poly cats=first type=line >> > >> d.vect -c map=streams_poly >> > >> >> > >> So what would be needed here is some kind of tool that connects all >> > >> touching lines and assigns a common category value, similar to the >> > >> v.dissolve tool for polygon features. I can imagine that such a task >> > >> might be not that uncommon also in another context? Any suggestions >> > >> how to achieve this in GRASS? >> > >> >> > >> A workaround that came into my mind was to create buffers around >> > >> lines in order to make areas out of lines. Subsequently these >> > >> touching areas can be merged using v.dissolve and the information >> > >> about the common category can be queried using v.distance. >> > >> Nevertheless, a rather cumbersome way to just assign a common >> > >> category value to all lines that are touching... >> > >> >> > >> Any further ideas? >> > >> >> > >> cheers, >> > >> >> > >> Johannes >> > >> >> > >>> >> > >>>> Cheers, >> > >>>> Johannes >> > >>>> >> > >>>> _______________________________________________ >> > >>>> grass-user mailing list >> > >>>> grass-user@lists.osgeo.org <mailto:grass-user@lists.osgeo.org> >> > >>>> https://lists.osgeo.org/mailman/listinfo/grass-user >> > >>> >> > _______________________________________________ >> > grass-user mailing list >> > grass-user@lists.osgeo.org >> > https://lists.osgeo.org/mailman/listinfo/grass-user
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