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

[Paulo van Breugel]

Check out the r.growth.shrink addon.

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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