[GRASS-user] r.neighbors with a custom mode calculation?

[Don MacQueen]

Glynn, Wolf,

Sorry to take so long to respond -- both of your solutions are just 
what I needed.
Thank you very much.

-Don

At 3:00 AM +0000 3/9/10, Glynn Clements wrote:
>Don MacQueen wrote:
>
>>  I'm pretty new to GRASS, and would appreciate some 
>>help/guidance/suggestions:
>>
>>  I have been smoothing a raster with r.neighbor, as in this example:
>>
>>     r.neighbors input=alandcov at PERMANENT output=alandcov_smooth
>>  method=mode size=45 {title=Smoothed}
>>
>>  The raster values are integers representing qualitative categories.
>>
>>  I'd like to modify the smoothing to exclude a particular value.
>>  Specifically, if a cell (is that the right term?) has a particular
>>  value, say 11, then I want to exclude it, as follows:
>>
>>    -  if the center of the neighborhood = 11, leave it unchanged (do
>>  not calculate the mode, just return 11)
>>    -  if the center is not 11, calculate the mode, but exclude any
>>  points in the neighborhood whose value = 11 (that is, take the mode
>>  only of points not equal to 11)
>>
>>  The real goal is to preserve boundaries between 11 and not 11. This
>>  is a land cover raster; 11 represents water, and I would like the
>>  smoothing to not change water to land or vice versa.
>>
>>  It seems like it might be possible to do it by creating a mask,
>>  smoothing the masked raster, and then putting the 11's back in maybe
>>  using r.mapcalc, but the details are a bit tough for me to put
>>  together, as a GRASS newbie.
>
>r.mapcalc 'elevens = if(alandcov == 11,11,null()) ; others = 
>if(alandcov == 11,null(),alandcov)'
>r.neighbors input=others output=alandcov_tmp  method=mode size=45
>r.mapcalc 'alandcov_smooth = if(not(isnull(elevens)),elevens,alandcov_tmp)'
>g.remove rast=elevens,others,alandcov_tmp
>
>--
>Glynn Clements <glynn at gclements.plus.com>


At 8:08 AM +0200 3/9/10, Wolf Bergenheim wrote:
>On Tue, Mar 9, 2010 at 02:30, Don MacQueen <macq at llnl.gov> wrote:
>>  The real goal is to preserve boundaries between 11 and not 11. This is a
>>  land cover raster; 11 represents water, and I would like the smoothing to
>>  not change water to land or vice versa.
>>
>>  It seems like it might be possible to do it by creating a mask, smoothing
>>  the masked raster, and then putting the 11's back in maybe using r.mapcalc,
>>  but the details are a bit tough for me to put together, as a GRASS newbie.
>
>To create the mask you can use
>r.mapcalc 'MASK=if(landcov==11,1,null())
>
>Then after you are done with whatever work you want to do, you can do
>this to put the water back like this
>r.mapcalc 'final=if(isnull(result)),11,result)'
>
>Hope this helps,
>Wolf
>
>--
><8  )---- Wolf Bergenheim ----(  3>


-- 
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Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062
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