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<div class="moz-cite-prefix">On 14/04/2019 14:11, Nicolas Cadieux
wrote:<br>
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<blockquote type="cite"
cite="mid:DA621C9C-2AF0-4375-81F3-16EC14FD079C@archeotec.ca">
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<div dir="ltr">Hi Micha,</div>
<div dir="ltr"><br>
</div>
<div dir="ltr">Great ideas, thanks. I was trying to get the
v.drape to work in Qgis but I was getting errors. I figure it’s
bad topology. I will fix it and try again directly in Grass. I
did manage to get the end nodes and start nodes. That has not
easy as the vectorizing was done in very small sections. I was
surprised to see so little merging tools that could</div>
</blockquote>
<p><br>
</p>
<p>You might want to simplify the rivers first. (v.generalize)</p>
<p> <br>
</p>
<blockquote type="cite"
cite="mid:DA621C9C-2AF0-4375-81F3-16EC14FD079C@archeotec.ca">
<div dir="ltr"> deal with this without manually selecting the
lines. I tried with an old Qgis 2.18 plugin but it was not
working properly.</div>
<div dir="ltr"><br>
</div>
<div dir="ltr">Your work flow is similar than what I had in mind
but the detail you gave will most certainly be useful.</div>
<div dir="ltr"><br>
</div>
<div dir="ltr">Nicolas</div>
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<div dir="ltr"><br>
Le 14 avr. 2019 à 02:24, Micha Silver <<a
href="mailto:tsvibar@gmail.com" moz-do-not-send="true">tsvibar@gmail.com</a>>
a écrit :<br>
<br>
</div>
<blockquote type="cite">
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<p>Here's an idea, using GRASS, that might get you started.</p>
<p><br>
</p>
<p>First use the v.drape module to convert your river network
to a 3D grass vector. Now add X,Y,Z coordinates to all start
and end points for all river sections with v.to.db. With
that you can extract those river sections where the Z value
of the endpoint is greater than the Z of the start point.
Finally, with v.edit, slip only those river sections.</p>
<p><br>
</p>
<p>Putting it all together. This is untested, use at your own
risk :-)</p>
<p><br>
</p>
<p>v.in.ogr input=rivers.shp output=rivers</p>
<p>r.in.gdal input=srtm.tif output=srtm</p>
<p>g.region -ap vect=rivers res=30 # Assuming the SRTM is 1
arcsec, or 30 m resolution</p>
<p><br>
</p>
<p># Make 3D rivers vector<br>
</p>
<p>v.drape input=rivers output=rivers_3d elev=srtm</p>
<p><br>
</p>
<p># Add X,Y,Z for start and end points<br>
</p>
<p>v.db.addcolumn map=rivers_3d columns="start_x DOUBLE,
start_y DOUBLE start_z DOUBLE, end_x DOUBLE end_y DOUBLE
end_z DOUBLE"</p>
<p>v.to.db map=rivers_3d option=start
columns="start_x,start_y,start_z"</p>
<p>v.to.db map=rivers_3d option=end
columns="end_x,end_y,end_z"</p>
<p><br>
</p>
<p># Flip only those river sections that are in wrong
direction</p>
<p># Add the "snap" tool along the way to make sure line
segments are indeed connected<br>
</p>
<p>v.edit rivers_3d tool=flip,snap where="end_z>start_z"
thresh=10<br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 13/04/2019 23:31, Nicolas
Cadieux wrote:<br>
</div>
<blockquote type="cite"
cite="mid:718dfc82-b3b9-a816-cea1-ea2e3e8dd9ee@archeotec.ca">Hi,
<br>
<br>
I have a difficult problem. I have a very large river
network file made with a 2D shapefile. (I have the SRTMs
for the same region). I would like to model a river network
but I need to keep in mind the river flow direction.
Unfortunately, I think this file was manually digitized and
therefore, line directions have no relationship with river
flow direction. <br>
<br>
Can anyone suggest a way to use my SRTMs to change the line
directions or to add a flow direction variable without
resorting to manually editing the layer? <br>
<br>
Thanks, <br>
<br>
Nicolas <br>
<br>
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<pre class="moz-signature" cols="72">--
Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918</pre>
</div>
</blockquote>
</blockquote>
<pre class="moz-signature" cols="72">--
Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918</pre>
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