[GRASS-dev] [GRASS GIS] #2016: v.surf.idw: very incorrect results

[GRASS GIS]

#2016: v.surf.idw: very incorrect results
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 Reporter:  hamish      |       Owner:  grass-dev@…              
     Type:  defect      |      Status:  new                      
 Priority:  major       |   Milestone:  6.4.4                    
Component:  Vector      |     Version:  svn-develbranch6         
 Keywords:  v.surf.idw  |    Platform:  Linux                    
      Cpu:  x86-64      |  
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Comment(by hamish):

 Hi,

 some more screenshots showing results of r.plane* + v.random + v.surf.idw,
 including some derivative maps from r.slope.aspect (devbr6). The 1000
 vector sampling points created by v.random are shown as black dots.

 [*] trend-plane created by the r.cog addon for spearfish's elevation.dem

 this example is not completely wrong (as is the case in the earlier
 attached screenshot!), just a net of overlain noise on top. So there could
 be two bugs here.

  - http://bambi.otago.ac.nz/hamish/grass/bugs/v.surf.idw/vsurfidw.png
  -
 http://bambi.otago.ac.nz/hamish/grass/bugs/v.surf.idw/vsurfidw.slope.png
  -
 http://bambi.otago.ac.nz/hamish/grass/bugs/v.surf.idw/vsurfidw.pcurv.png
  -
 http://bambi.otago.ac.nz/hamish/grass/bugs/v.surf.idw/vsurfidw.tcurv.png

 note the strands of noise in the NW corner in the curvature maps, and the
 clump of it the center-right of the lower edge in the slope map. Try to
 match them with the r.surf.idw slope map below.

 ----
 for comparison, same-data slope map from v.surf.rst and r.surf.idw
 modules.

  -
 http://bambi.otago.ac.nz/hamish/grass/bugs/v.surf.idw/vsurfrst.slope.png
  -
 http://bambi.otago.ac.nz/hamish/grass/bugs/v.surf.idw/rsurfidw.slope.png

 r.surf.idw2 was very similar, but not identical, to r.surf.idw; so not
 shown.
 As expected, v.surf.rst is much smoother throughout although it suffers
 from edge-effects and stitching of the quadtree segmentation around the
 edges. This suggests the quadtree vector map should be created and the
 outer row of segments from it discarded.


 Hamish

-- 
Ticket URL: <https://trac.osgeo.org/grass/ticket/2016#comment:2>
GRASS GIS <http://grass.osgeo.org>