I need to calculate the values for the 25%, 50%, 75% and 90% quantile over a series of rasters (time series of ndvi values from landsat). I am exploring the r.series command in Grass GIS, but the documentation is very poor and it doesn't seem to fit my needs.
I would need to calculate out of the overall distribution of values in the 12 monthly ndvi images the indicated quantile. I just need the values, not a map.
Any idea on the matter? Anyone can actually explain me what method=quantile actually does in r.series on grass gis?