Hello Martin, I was suggesting that using a shapefile does not provide much help in these cases and that using a geodatabase could be the way to go. QGIS provides a very powerful "personal geodatabase", spatialite. Just go here: https://www.gaia-gis.it/fossil/libspatialite/wiki?name=misc-docs for documentation. I'm very fond of the Cookbook which is not at all a complete guide to geodatabase, but it's something you may use to learn the basics (and more) in an afternoon.
Ciao c On Wed, 15 Jul 2015 at 22:50:37, Martin Bain <[email protected]> wrote: > Ciao Carlo, > I'm a new QGIS user, I'm intrigued by your last paragraph: > > You may also assume some "intelligence" in the tools you use may provide > som help. It's more convenient to keep your streams in a network conscious > database like spatialite instead of storing into shapefiles. > > Can you elaborate on the meaning of "network conscious database" or point > me to some links to get me started, this sounds like a very useful > capability. > > Martin. > > > From: [email protected] [mailto: > [email protected]] On Behalf Of Carlo A. Bertelli (Charta > s.r.l.) > Sent: Wednesday, 15 July 2015 4:24 PM > To: [email protected] > Subject: Re: [Qgis-user] rivers growing in size as they go downhill > > Ciao Luca, > if you mean cutting the stream and manually assigning a width to every > arc, well, it's not the right procedure anyway, but if you deal with a > network as a network you should allow waterflow grow for other reasons > besides going downhill. Every node brings affluents so more water becomes a > bigger stream. So classifying the rank of the network is the proper thing > to do. You don't have to do it manually, it's a directed planar graph so > there are tools to deal with it (plugings and processing). > If you look at old cartography, you may argue streams grow gradually and > that is true, but there are tiny gutters and invisible kennels feeding > them... > Yes you may desire to kill all hydrologists, but this is a graph and the > easiest thing is assuming the size of the stream depends on the rank of the > starting node. > You may also assume some "intelligence" in the tools you use may provide > som help. It's more convenient to keep your streams in a network conscious > database like spatialite instead of storing into shapefiles. > c > > On Tue, 14 Jul 2015 at 22:08:45, <[email protected]<mailto: > [email protected]>> wrote: > Dear all > i have this idea of rendering a river network so that each river starts as > a very thin blue line, and the line width increases little by little as the > river goes. > i wouldn't like to modify the original file (eg cutting rivers in pieces > and give a different width to each piece) but all rivers are digitized with > the right direction so i was wondering if there is an expression to teach > qgis what is the start end of a river, and assign a wider line for any > given distance, for example: > from start to 200m - line width 0.1 > from 200m to 400m - line width 0.2 > from 400m and over - line width 0.3 > i think this is an interesting problem because i cannot find a "from - to" > command in qgis expression language, neither i know how to properly exploit > the line direction with code, which would come useful in many other ways... > any python expert out there can help? > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://lists.osgeo.org/pipermail/qgis-user/attachments/20150714/53ba1c74/attachment-0001.html > > >
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