Then, according to {HEAD ~ the distances} d3, d4 and other known parameters, {TAIL ~ the position} of the touch point C can be calculated 
Then , according to { HEAD ~ the distances } d3 , d4 and other known parameters , { TAIL ~ the position } of the touch point C can be calculated
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH