Hello Ivan, AFAIU you could use the slope and offset maps from t.rast.series within t.rast.algebra to detrend the values of the maps within the strds, something like "detrended_strds = trend_strds - (trend_strds*map(slope) + map(offset))". Others suggest, to detrend by subtracting the previous value, i.e. that would imply using the temporal algebra with the temporal index, something like "detrended_strds = trend_strds[1] - trend_strds[0]".
I haven't tested any of these, just a couple of ideas ;-) However, I do not know how this might interact with seasonality within data, or irregular gaps. hth somehow Vero El vie, 22 dic 2023 a las 5:10, Ivan Marchesini via grass-user (< grass-user@lists.osgeo.org>) escribió: > Dear colleagues > > I would like to the advantage of the t.* modules for detrending a strd. > > In the strd I have earth observation data irregularly sampled (2 or 3 > times per month), in the period November-February, for 7 years. They are > not equally spaced (i.e gaps have different duration) > > A simple t.rast.series analysis (opion=slope,offset) highlights that > probably there is a descending trend when considering the maps ordered > by id. > > I would like to fit a proper time depending fitting curve for each pixel > and then subtract the function from the real data. > > any hints on how I can do this task exploiting the GRASS GIS modules or > some simple bash/python scripting? > > thank you > > Ivan > > > > > _______________________________________________ > grass-user mailing list > grass-user@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/grass-user >
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