[Qgis-user] rivers growing in size as they go downhill

[Carlo A. Bertelli (Charta s.r.l.)]

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 <Martin.Bain at lismore.nsw.gov.au>
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: qgis-user-bounces at lists.osgeo.org [mailto:
> qgis-user-bounces at lists.osgeo.org] On Behalf Of Carlo A. Bertelli (Charta
> s.r.l.)
> Sent: Wednesday, 15 July 2015 4:24 PM
> To: qgis-user at lists.osgeo.org
> 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, <luca.galuppini at gmail.com<mailto:
> luca.galuppini at gmail.com>> 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?
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