R help - Apr 2008 - extracting averages from smooth.ppp output on spatstat

I have used smooth.ppp in spatstat to create a smoothed surface plot based
on randomly selected depths across a lake (as marks).

I wonder if based on the smoothed surface plot if I can calculate the
average depth for each 10x10 grid square across the lake.

I can't see any obvious way of doing this and would appreciate some
pointers.

Many thanks,

Graham

	[[alternative HTML version deleted]]