[Qgis-user] Manipulating DEM

[Kirk Schmidt]

Hi Ulli:

If I understand your project correctly, you only have the post DEM and 
you want to remove the new trench so that you can perform some 
additional analysis.  SO, off the top of my head, I would digitize a 
polygon whoch defines the extent of the trench.  I would use this 
polygon to erase the points derived from the contour lines and then 
create your DEM from the resulting pointg layer without elevations 
inside the trench.  You can try different techniques for creating the 
dem using the saga griding functions within the processing toolbox.  By 
using a TIN approach, the result may be a bit blocky.  If yopu try a 
B-spline interpretation, the results will be smoother, however 
individual elevations are interpreted along a spline and therefore may 
over or underestimate the actual elevations.

Hope this helps


Kirk

On 11/8/2018 9:49 AM, Ulrich Kriechbaum wrote:
> Dear all!
> I investigate a Glacial-Lake Outburst Flood and try to back-calculate 
> the event using the simulation tool r.avaflow. During the event there 
> was a big trench eroded. I have a post-event DEM with a clearly 
> visible eroded trench. What i want to do now is to "flatten" out the 
> trench so that i get a pre-event DEM to start my simulation. What i 
> tried to do is to create the contour lines of the post-event DEM, 
> change them so that they would not show the trench and then create a 
> pre-event DEM out of this contour lines. I already asked the question, 
> if anyone knows how to do that, i already got some nice answers but 
> unfortunately none of the inputs really work for me....
> So now to my actual question: Does anyone know another method how to 
> "flatten" out the trench in the DEM? I would be really glad if someone 
> would have an answer, as i have ben struggling a while now with these 
> problem..
> Best regards,
> Ulli
>
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-- 
Kirk Schmidt, MScF, BScF, RPF
General Manager
Nortek Resource Solutions Inc.
RR # 1
Thorburn, NS
B0K 1W0
Tel (902) 922.3607
Email: kirk at nortekresources.com
Web: www.nortekresources.com

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