I am trying to understand the behaviour of ST_Intersects() in PostGIS.
My goal is to get the mean value of a raster area corresponding to each polygon in a vector layer.
To test my SQL I run initially the script with a vector layer containing only one geometry:
CREATE TABLE mean AS SELECT id, (ST_SummaryStats(ST_Clip(rast,1,geom))).mean FROM vector, raster WHERE ST_Intersects(geom,rast)
What returns is a two rows table:
How it is possible that the same geometry intersects the same raster twice with two different values?
I don't know if it is a coincidence, but the mean value I got doing the same operation with the same two layers with the QGIS Zonal Statistics is -138.788659793814 (the mean between -146.258943781942 and -115.587301587302 is -130... pretty close)