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