[GRASS-dev] [GRASS GIS] #2526: extend r.slope.aspect to compute the values at the edges

[GRASS GIS]

#2526: extend r.slope.aspect to compute the values at the edges
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 Reporter:  hellik       |       Owner:  grass-dev@…              
     Type:  enhancement  |      Status:  new                      
 Priority:  normal       |   Milestone:  7.1.0                    
Component:  Raster       |     Version:  svn-trunk                
 Keywords:  slope        |    Platform:  All                      
      Cpu:  All          |  
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Description changed by neteler:

Old description:

> taken from the ML
>
> http://lists.osgeo.org/pipermail/grass-dev/2015-January/072779.html
>
> {{{
> Another way would be to modify r.slope.aspect to compute the values at
> the edges - a second order polynomial min.square approximation
> is used to estimate the derivatives in r.slope.aspect (you get the well
> known differencing function when you do the math) and it can be used also
> to compute the values at the edge cells, but I had no luck convincing
> others that it is the right thing to do.
>
> I believe that any reasonable estimate is better than the current
> shrinking region (in r.flow we just propagate the same values to the
> edges), but that does not seem to be the consensus.
>
> Also, implementation  for the edges is not straightforward because of how
> GRASS works with rows, but a smart developer could certainly do it.
> }}}
>
> it would be nice that r.slope.aspect compute the values at the edges, at
> least as an option. I agree that any reasonable estimate is better than
> the current shrinking region.

New description:

 taken from the ML

 http://lists.osgeo.org/pipermail/grass-dev/2015-January/072779.html


 Helena Mitasova - Sun Jan 4 06:36:27 PST 2015

 ''Another way would be to modify r.slope.aspect to compute the values at
 the edges - a second order polynomial min.square approximation is used to
 estimate the derivatives in r.slope.aspect (you get the well known
 differencing function when you do the math) and it can be used also to
 compute the values at the edge cells, but I had no luck convincing others
 that it is the right thing to do.''

 ''I believe that any reasonable estimate is better than the current
 shrinking region (in r.flow we just propagate the same values to the
 edges), but that does not seem to be the consensus.''

 ''Also, implementation  for the edges is not straightforward because of
 how GRASS works with rows, but a smart developer could certainly do it.''


 ----
 It would be nice that r.slope.aspect compute the values at the edges, at
 least as an option. I agree that any reasonable estimate is better than
 the current shrinking region.

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Ticket URL: <http://trac.osgeo.org/grass/ticket/2526#comment:1>
GRASS GIS <http://grass.osgeo.org>