[GRASS-user] Median filtering time series in time only

[Veronica Andreo]

What exactly do you mean by median-filtering in time only, Nikos? Get the
median and then filtering out all pixels above/below that value? If that's
the case, then maybe some of the examples here
https://grasswiki.osgeo.org/wiki/Temporal_data_processing#Spatio-temporal_algebra_with_STRDS
might be of help

Basically, you first estimate the median of the series (or the period you
are interested in) either with r.series or t.rast.series and then use
t.rast.mapcalc or t.rast.algebra to get only pixels below/above that value
represented pixelwise in the median map. It can also be a single value of
course.

Does that make sense?

best,
Vero


El mié., 27 ene. 2021 08:44, <nik at nikosalexandris.net> escribió:

> I am trying to median-filter time series in time and not in space.
>
> Not sure `r.series.filter` is the right tool.
> I skimmed through the manual, the paper and the source code. Yet I am
> asking for a confirmation.
> Its (odd integer) parameter `winsize=` implies a moving window (of size
> winsize^2).
> Does this rather filter images, of a time series, in space?
> Or does the `winsize` here refer to the length of a moving temporal
> window?
>
> Then, there is `r.series.lwr`.
> Can I use the tool with `order=0` and `delta=1` (or `order=3` and
> `delta=1`)
> and perform a moving average filtering in time?
> It's not median. Still I'd like to see a filtering in time-only effect.
>
> And, now I recall `r.hants`.
> Is there a way to use it for filtering-out only lows and highs (`-l` and
> `-h` respectively) pixel-wise in time, without interpolating nor
> extrapolating?
>
> Else, I guess there should be a way to build a 'custom' filter using
> `t.rast.algebra` using its temporal neighborhood modifier.
> It's convenient if one the tools above does already median-filtering in
> time-only.
>
> Kind regards, Nikos
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