[Qgis-user] Removing artifacts in a created DEM

[Nicolas Cadieux]

Hi, 
I would go with the TIN if your points are far apart. That will not create the bumps that you see.  IDW is good but you may have to change the IDW weights from 2 (1\2, the typical gravity model) to 3 or 4 to smooth thing out.  Be careful and make sure you original values don't shift too much.  NN is very good if you have a very high density of sampling points (like LiDAR), at least in regards to the way it is implemented by GDAL. 
Nicolas Cadieux M.Sc. 
Les Entreprises Archéotec inc.  
8548, rue Saint-Denis Montréal H2P 2H2 
Téléphone: 514.381.5112  Fax: 514.381.4995 
www.archeotec.ca 
On Oct 17, 2015 03:29, "Andreas Neumann [via OSGeo.org]	" <ml-node+s1560n5230817h88 at n6.nabble.com> wrote: 

	
  
    
  
  
    Hi Hernan, 
    
    I think neither of the methods you used give good results for
    interpolating terrain data (or most other interpolations). 
    
    I had good results with v.surf.rst (available in the Processing
    toolbox in the GRASS section). There are tons of options with the
    v.surf.rst - but the defaults probably work for most options. You
    also don't have to output all the raster results - just the
    interpolated surface. 
    
    One of the other options is the "Interpolation plugin" which comes
    with QGIS (but you have to enable it in QGIS). It appears in the
    raster menu in as "Interpolation". It offers a TIN interpolation and
    IDW. I think the TIN method is the more interesting one. 
    
    Hope this helps, 
    Andreas 
    
    On 17.10.2015 00:21, hersala wrote: 
    
    
      
        Hello, 
        
        
        
        I'm working with a bundle of N-S and E-W distributed DGPS
          point transects on gentle glacier slope. With these points I
          created a shp file and then I obtained several DEMs (.tif
          files) using the tool Raster/Analysis/Grid (Interpolation). 
        I've used Nearest Neighbor, Runing Means and Inverse
          Distance with several argument values. Inverse Distance
          produces the best results, but there are some artifacts that
          persists and makes the output unusable. They give the
          impression as if the glacial slope has bumps, but on the
          contrary, it is quite gentle. 
        
        
        Can anyone give any advice in how to proceed to reduce such
          artifacts. 
        
        
        I'm using QGIS 2.8.2-Wien in MS-Windows. 
        
        
        Thanks in advance. 
        
        
        Hernan 
        
        
      
      
      
      
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