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

[Markus Metz]

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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>
>
>
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