[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):

 further comments on GRASS65 version,
 I looked again at the negative values and according to the manual:Negative
 numbers indicate that those cells possibly
 have surface runoff from outside of the current geographic region.

 However, when running r.watershed with elev_lid792_1m in the nc_spm_08
 data set I get this as the result for mfd (which looks great):
 http://skagit.meas.ncsu.edu/~helena/grasswork/accum_mfd.png
 [[BR]]

 but this is where the negative values are:
 http://skagit.meas.ncsu.edu/~helena/grasswork/accum_mfd_neg.png
 [[BR]]
 why does it switch from positive to negative in the middle
 of the slope even for the flow accumulation that apparently originates
 on the top of the hill well inside the area?
 Am I somehow misinterpreting the results?
 I can imagine the high accumulation values starting from outside,
 but the low negative accumulation values (in tens of cells) close to the
 center
 of the region have no way of starting outside.
 [[BR]]
 Helena
 [[BR]]

 Just a note that the man page has description and option twice,
 this should be an easy fix.

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Ticket URL: <http://trac.osgeo.org/grass/ticket/807#comment:11>
GRASS GIS <http://grass.osgeo.org>