[postgis-users] Raster cell size and wrong mean value calculation problem

[Pierre Racine]

> The raster cells with the same elevation value got merged, why?

Because intersecting with every single pixel outline would be just too long.

> The mean value which based on the actual result cannot be correct. 

You actually want to compute a weighted mean, not simply a mean. The weighted mean give a correct result (actually more accurate than the clip option but requiring more geometric processing).

Have a look at the tutorial which is now a little bit old:

http://trac.osgeo.org/postgis/wiki/WKTRasterTutorial01

The other way is as Bborie said. ST_Clip() the raster and ST_SummaryStat().

Pierre