[GRASS-user] dilation & erosion (mathematical morphology)

[Robert Nuske]

Hi Markus,

is there a chance that this patch (or r.grow shrinking patches if radius is 
negative) will land in relbr70?


cheers,
  robert


On Thursday 05 February 2015 22:13:32 Markus Metz wrote:
> On Thu, Feb 5, 2015 at 2:53 PM, Paulo van Breugel
> 
> <p.vanbreugel at gmail.com> wrote:
> > Check out the r.growth.shrink addon.
> 
> See also ticket #2368 [0] which includes a patch for r.grow.distance
> to shrink (distance from nearest NULL cell to be precise).
> 
> Markus M
> 
> https://trac.osgeo.org/grass/ticket/2368
> 
> > On Thu, Feb 5, 2015 at 1:59 PM, Robert Nuske <rnuske at gwdg.de> wrote:
> >> Hi there,
> >> 
> >> looking at some noisy raster map, I would like to clean up the patches
> >> (map
> >> consists only of one class and NULL) using basic mathematical morphology
> >> (dilation & erosion) in GRASS 7.0.
> >> 
> >> 
> >> The dilation can easily be achieved with r.grow.
> >> But the erosion seems not to be as straight forward.
> >> 
> >> Since the example about shrinking was removed from the help page of
> >> r.grow
> >> in
> >> GRASS 7.0 (http://grass.osgeo.org/grass70/manuals/r.grow.html), I hoped
> >> for an
> >> easier way to carry out the erosion. Looking in vain for a raster command
> >> named shrink or erode, I tried a negative distance in r.buffer (-> error)
> >> and
> >> negative radius in r.grow (treated as absolute value).
> >> 
> >> The following produce identical output with grown patches.
> >> 
> >>   r.grow in=mod_10_33 out=mod_10_33_1 radius=1.1
> >>   r.grow in=mod_10_33 out=mod_10_33_2 radius=-1.1
> >> 
> >> Any suggestions for a quick erosion?
> >> 
> >> 
> >> thanks
> >> 
> >>   Robert
> >> 
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