<div>Hi there,</div>
<div> </div>
<div>I don't know how to help but I believe that Achim</div>
<div>have, for each pixel of stream, one value like 1, 2, 4, 8, 16, 32, 64 and 128,</div>
<div>and each of these values can be set to only one of 8 possible directions.</div>
<div> </div>
<div>Milton<br>brazil=toronto<br></div>
<div class="gmail_quote">2009/5/20 achim <span dir="ltr"><<a href="mailto:ak7@jupiter.uni-freiburg.de">ak7@jupiter.uni-freiburg.de</a>></span><br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">Thanks for reply,<br><br>but thats not exactly what I am searching for. I can not to use the<br>accumulation values, because<br>
<br><br>i) I want to figure out the watersheds on parts of the network<br>(beginning from certain points of the river network to separate some<br>basins on different levels; I already wrote a script to do it with the<br>direction raster map, but its slow and it does not allow me to do ii)<br>
<br>ii) I am going to do some statistics on stream lengths /accumulations on<br>network parts<br><br>iii) I need to separate parallel flowing streams from each other which<br>does not work on my current resolution<br><br>
<br>I start with pre-produced flow direction, accumulation...<br><br>Any workaround idea or scripting tips?<br><br>cheers again,<br>achim<br><br><br>PS: illustration on<br>
<div class="im"><a href="http://lists.osgeo.org/pipermail/grass-user/attachments/20090520/6198f353/rasterflow-to-network.png" target="_blank">http://lists.osgeo.org/pipermail/grass-user/attachments/20090520/6198f353/rasterflow-to-network.png</a><br>
<br></div>PPS:<br>
<div class="im">> r.mapcalc 'log_accumulation=log(abs(accumulation)+1)'<br></div>QUESTION:<br>why abs? accumulation values should be positive!?<br><br>Margherita Di Leo schrieb:<br>
<div>
<div></div>
<div class="h5">> Hi Achim,<br>><br>> i usually produce the river network starting from the flow accumulation,<br>> not from the flow direction. If you have a raster elevation map you can<br>> get it using r.watershed.<br>
> Then, i make as follows:<br>><br>> r.mapcalc 'log_accumulation=log(abs(accumulation)+1)'<br>><br>> r.mapcalc 'inf_river=if(log_accumulation>6)'<br>><br>> 6 is a treshold value for the log_accumulation, it is a good value for<br>
> me but you maybe can try other values. It produces a binary map.<br>><br>> Then:<br>><br>> Raster -> Transform features -> Thin linear features to reduce at 1pixel<br>> the lines of the binary raster inf_river and create the new file in_river.<br>
> Finally, with r.to.vect you can transform the raster in_river in a<br>> vector map.<br>><br>> Hope this helps<br>><br>> Margherita<br>><br>>> Message: 8<br>>> Date: Wed, 20 May 2009 16:45:56 +0200<br>
>> From: achim <<a href="mailto:ak7@jupiter.uni-freiburg.de">ak7@jupiter.uni-freiburg.de</a>><br>>> Subject: [GRASS-user] IN: raster-flow-direction OUT:vector-network?<br>>> To: grass-user <<a href="mailto:grass-user@lists.osgeo.org">grass-user@lists.osgeo.org</a>><br>
>> Message-ID: <<a href="mailto:4A1417A4.3040701@jupiter.uni-freiburg.de">4A1417A4.3040701@jupiter.uni-freiburg.de</a>><br>>> Content-Type: text/plain; charset="iso-8859-15"<br>>><br>>> Hello,<br>
>><br>>> I am searching for a good idea to convert a raster-flow-direction map<br>>> into a vector-network map.<br>>><br>>> Probably I will have to write a script. If it is possible at all...<br>
>><br>>> In case of writing a script it mean to me: how to produce a line within<br>>> r.mapcalc?<br>>><br>>> Has anyone a hint?<br>>><br>>> Cheers,<br>>> achim<br>>><br>
>> PS:for illustration I attached a little picture<br>>> -------------- next part --------------<br>>> A non-text attachment was scrubbed...<br>>> Name: rasterflow-to-network.png<br>>> Type: image/png<br>
>> Size: 5162 bytes<br>>> Desc: not available<br>>> Url :<br>>> <a href="http://lists.osgeo.org/pipermail/grass-user/attachments/20090520/6198f353/rasterflow-to-network.png" target="_blank">http://lists.osgeo.org/pipermail/grass-user/attachments/20090520/6198f353/rasterflow-to-network.png</a><br>
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