A scatterometer for the investigation of surface quality causes a radiation beam with a well-defined direction to fall upon a sample under test. More particularly, the extraction may be achieved by using iterated graph cuts. Alternatively, the control unit obtains slope ascending information or slope descending information of the road by making use of a driver operation panel or a bus location system. The level detection circuit operates in a demand-controlled mode responsive to the pump-boost signal being active to develop the pump activation signal to activate the voltage pump responsive to the output voltage being less than or equal to a second low threshold value. Movement of the second plate relative to the first plate selectively opens or closes the pathway for the granular material from the hopper through the discharge port and onto the fan.