That is, because optical data give {HEAD ~ sgood results} at short distances, if both optical data and SATPS data are available, and if the distance is less than {TAIL ~ a predetermined threshold} , optical data is used 
That is , because optical data give { HEAD ~ sgood results } at short distances , if both optical data and SATPS data are available , and if the distance is less than { TAIL ~ a predetermined threshold } , optical data is used
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH