The SAGA Raster Calculator within QGIS produces wrong results probably due to interpolation but works corretly withion SAGA itself. The problem has been discussed here before but sofar I have not found any useful solution. see also: Why does SAGA raster calculator interpolate between cell values? Raster calculators in SAGA return incorrect results). Why does interpolation (?) occur and how can it be avoided? I need the raster calculation to be performed within a QGIS python script.