[GRASS-dev] Re: [GRASS GIS] #807: r.watershed doesnt consider longer distance to diagonal neighbouring pixels

[GRASS GIS]

#807: r.watershed doesnt consider longer distance to diagonal neighbouring pixels
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  Reporter:  aread   |       Owner:  grass-dev at lists.osgeo.org
      Type:  defect  |      Status:  new                      
  Priority:  major   |   Milestone:  6.4.0                    
 Component:  Raster  |     Version:  6.4.0 RCs                
Resolution:          |    Keywords:  r.watershed              
  Platform:  All     |         Cpu:  All                      
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Comment (by helena):

 I finally had chance to look at it and it does make a significant
 difference (much more than I would have ever guessed)
 and I think that after some more testing
 the fix should go to the GRASS64 release as a bugfix.

 Some examples from the nc_spm_08 data set
 1m resolution
 old

 http://skagit.meas.ncsu.edu/~helena/wrriwork/lakewh/flowD8dem.jpg

 new

 http://skagit.meas.ncsu.edu/~helena/grasswork/accum_5Kdiagfix.png

 red is the stream from high res ortho

 http://skagit.meas.ncsu.edu/~helena/grasswork/accum_5Kdiagfix2.png.png

 I haven't done any serious testing but brief visual comparison indicates
 that the fix may improve the accuracy of stream extraction beyond
 just looking more realistic)
 red-sreams from ortho, blue-old, black-new

 http://skagit.meas.ncsu.edu/~helena/grasswork/accum_diagfix_streams.png

 example with the 30m ned shows quite a few differences -
 see the first stream from the west on these two images with the fix
 apparently better although still with some error:

 http://skagit.meas.ncsu.edu/~helena/grasswork/accum_10Korig.png

 http://skagit.meas.ncsu.edu/~helena/grasswork/accum_10kfix.png

 It would be very useful if anybody who has some other data than nc_spm and
 some orthos to compare the results with runs another test and confirms
 that
 the change can go into 64, Markus, thanks for fixing it so quickly,

 Helena

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Ticket URL: <https://trac.osgeo.org/grass/ticket/807#comment:3>
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