[GRASS-dev] RFC: variations of statistics in r.neighbors (and the stats lib)

[Veronica Andreo]

Hello Francesco, Markus

I find the possibility of getting statistics for only a certain fraction of
a neighbourhood really interesting and I like Markus' idea as it is more
general and allows for more use cases 🤓 Count me in for testing ;)

Vero

El mar, 31 ene 2023 a las 15:48, Markus Metz (<markus.metz.giswork at gmail.com>)
escribió:

> Hi Francesco,
>
> the proposed change to r.neighbors is interesting, but maybe too specific:
> you have introduced two new functions, and many more functions would be
> needed to e.g. get the filtered standard deviation or median.
>
> Therefore I suggest adding some filtering option to r.neighbors consisting
> of a filtering function and a comparison operator. The filtering function
> would be any of the currently supported neighborhood functions returning
> some value. The comparison operator would be one of gt, ge, le, lt (>, >=,
> <=, <). r.neighbors would then first get the result value of the filtering
> function, then set all values in the neighborhood to NULL that do not
> fulfil the condition "value <comparison operator> <result value">, then
> call the actual neighborhood operation with the filtered values. This would
> be more flexible, because the user can freely combine a neighborhood filter
> function with a neighborhood operation.
>
> Makes sense?
>
>
> On Wed, Jan 25, 2023 at 10:55 AM Francesco P. Lovergine <
> frankie at debian.org> wrote:
>
>> Hi,
>>
>> for some specific needs of a research project, I had to make a little
>> change to r.neighbors (the target version was 7.8.5 but that's not
>> essential).
>>
>> Essentially, the idea behind is computing first order statistics on
>> partial
>> populations as identified by selected quantiles (samples >= or <= of a
>> threshold value of quantile).
>>
>> For that, I introduced average_ge_quantile and average_le_quantile
>> operators modes.
>>
>>
>> https://github.com/fpl/grass/commit/6b83795b037c6645a32d6a525cfdee3cc65d521c
>>
>> (the html file is still not updated)
>>
>> I'm not persuaded this is the most elegant way of doing this kind of
>> things,
>> maybe it would be better using an option (as in the case of -w for
>> weighted
>> operations) to compute average and possibly other statistics. Even, one
>> could
>> think in general to other multiple ways of selecting population on the
>> base of
>> quantiles/percentiles of population in a window.
>>
>> Any hint/opinion/alternative/critic about that?
>>
>> All this in the remote hypothesis that a pull request could have sense
>> for such a kind of features.
>>
>> Thanks
>>
>>
>> --
>> Francesco P. Lovergine
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