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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Ciao Carlo,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I’m a new QGIS user, I’m intrigued by your last paragraph:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Martin.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> qgis-user-bounces@lists.osgeo.org [mailto:qgis-user-bounces@lists.osgeo.org]
<b>On Behalf Of </b>Carlo A. Bertelli (Charta s.r.l.)<br>
<b>Sent:</b> Wednesday, 15 July 2015 4:24 PM<br>
<b>To:</b> qgis-user@lists.osgeo.org<br>
<b>Subject:</b> Re: [Qgis-user] rivers growing in size as they go downhill<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Ciao Luca,<o:p></o:p></p>
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<p class="MsoNormal">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).<o:p></o:p></p>
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<p class="MsoNormal">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...<o:p></o:p></p>
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<p class="MsoNormal">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.<o:p></o:p></p>
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<p class="MsoNormal">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.<o:p></o:p></p>
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<p class="MsoNormal">c<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Tue, 14 Jul 2015 at 22:08:45, <<a href="mailto:luca.galuppini@gmail.com">luca.galuppini@gmail.com</a>> wrote:<o:p></o:p></p>
<p class="MsoNormal">Dear all<br>
i have this idea of rendering a river network so that each river starts as<br>
a very thin blue line, and the line width increases little by little as the<br>
river goes.<br>
i wouldn't like to modify the original file (eg cutting rivers in pieces<br>
and give a different width to each piece) but all rivers are digitized with<br>
the right direction so i was wondering if there is an expression to teach<br>
qgis what is the start end of a river, and assign a wider line for any<br>
given distance, for example:<br>
from start to 200m - line width 0.1<br>
from 200m to 400m - line width 0.2<br>
from 400m and over - line width 0.3<br>
i think this is an interesting problem because i cannot find a "from - to"<br>
command in qgis expression language, neither i know how to properly exploit<br>
the line direction with code, which would come useful in many other ways...<br>
any python expert out there can help?<br>
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