[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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 Hi,

 I have noticed with some data very bad results with v.surf.idw. The
 r.surf.idw and r.surf.idw2 modules do ok with the same data after
 v.to.rast of the starting points. But the v.surf.idw results are not
 realistic both spatially and numerically.

 In my real data I was seeing bad slivering between sample sites, but can
 recreate other little-relation to source data weirdness with synthetic
 input.

 commands to make the attached screenshot in grass6:
 {{{
 g.region -d    # spearfish
 # from addons:
 r.surf.volcano out=gauss method=gaussian kurtosis=0.5 peak=5000
 r.random in=gauss vect=gauss_rand_500 n=500
 v.surf.idw in=gauss_rand_500 out=gauss_rand_500.vidw column=value
 }}}

 plot:
 {{{
 d.mon x0
 d.resize w=666 h=1006
 d.font Vera
 d.split.frame frames=2
 #
 d.frame uno
 MAP=gauss
 r.colors "$MAP" col=bcyr
 d.rast "$MAP"
 d.vect gauss_rand_500 icon=basic/point fcolor=none color=60:60:60
 d.legend "$MAP" at=5,60,2,5
 echo "$MAP" | d.text color=black size=4
 #
 d.frame dos
 MAP=gauss_rand_500.vidw
 r.colors "$MAP" col=bcyr
 d.rast "$MAP"
 d.vect gauss_rand_500 icon=basic/point fcolor=none color=60:60:60
 d.legend "$MAP" at=5,60,2,5
 echo "$MAP" | d.text color=black size=4
 }}}


 fwiw I also notice that the module does not scale well to large region
 sizes (at all).


 thanks,
 Hamish

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Ticket URL: <http://trac.osgeo.org/grass/ticket/2016>
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