focusing on {HEAD ~ each} of {TAIL ~ the reference plane datums} and generating a focus data for each datum; and 
of
focusing on { HEAD ~ each } of { TAIL ~ the reference plane datums } and generating a focus data for each datum ; and
OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH