These focus points are used to determine {HEAD ~ a best fit surface} for {TAIL ~ the virtual slide image} 
for
These focus points are used to determine { HEAD ~ a best fit surface } for { TAIL ~ the virtual slide image }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL