dividing {HEAD ~ an airspace} encompassing {TAIL ~ an initial point} and a destination point into a plurality of grid cells 
encompassing
dividing { HEAD ~ an airspace } encompassing { TAIL ~ an initial point } and a destination point into a plurality of grid cells
OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH