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