[GRASS-dev] [GRASS GIS] #2820: v.surf.idw results seem seriously wrong and don't match r.surf.idw results

[GRASS GIS]

#2820: v.surf.idw results seem seriously wrong and don't match r.surf.idw results
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  Reporter:  lrntct   |      Owner:  grass-dev@…
      Type:  defect   |     Status:  new
  Priority:  blocker  |  Milestone:  7.0.3
 Component:  Vector   |    Version:  7.0.1
Resolution:           |   Keywords:  v.surf.idw r.surf.idw interpolation
       CPU:  x86-64   |   Platform:  Linux
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Comment (by mlennert):

 Replying to [comment:8 pkelly]:
 > Hi Moritz, Thanks for bringing this to my attention. Looks like the bug
 with the squared distance was introduced when support for powers other
 than 2 was added in r32957, and ported to GRASS 7 in r59107.

 Indeed. Before that, no need to take the square root if it was to only
 square the distance afterwards...


 >
 > I haven't been able to test the example in the Trac ticket yet as I
 don't have GRASS 7 currently installed, only 6.4, and the GRASS6 version
 of the NC dataset at
 <https://grass.osgeo.org/sampledata/north_carolina/nc_spm_latest.tar.gz>,
 when uncompressed, seems to be actually the same as the GRASS7 version.

 Yes, that's a bug. Running v.build.all in the PERMANENT mapset solves that
 easily, though.


 > One thing I would consider testing first if I had the data, would be to
 enlarge the region to slightly bigger than the edges of the point cloud
 (i.e. slightly bigger than the result of g.region vect=stations_vect),
 just in case there were any rounding issues with points right at the edge
 falling out of the region and not being included in the indexing.

 The interpolation was done in a region defined by the nc_state boundary:

 {{{
 g.region vect=nc_state res=500 -ap
 projection: 99 (Lambert Conformal Conic)
 zone:       0
 datum:      nad83
 ellipsoid:  a=6378137 es=0.006694380022900787
 north:      318500
 south:      10500
 west:       124000
 east:       930500
 nsres:      500
 ewres:      500
 rows:       616
 cols:       1613
 cells:      993608
 }}}

 Setting the region with station data gives:


 {{{
 g.region vect=precip_30ynormals res=500 -a
 projection: 99 (Lambert Conformal Conic)
 zone:       0
 datum:      nad83
 ellipsoid:  a=6378137 es=0.006694380022900787
 north:      306500
 south:      27500
 west:       151500
 east:       917500
 nsres:      500
 ewres:      500
 rows:       558
 cols:       1532
 cells:      854856
 }}}

 so, I don't think that this is the issue, here.

 Moritz

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Ticket URL: <https://trac.osgeo.org/grass/ticket/2820#comment:9>
GRASS GIS <https://grass.osgeo.org>