{TAIL ~ The method} comprises illuminating the first object so as to produce a shadow of {HEAD ~ the first object} on a surface lying at a known position with respect to the second object and forming a two dimensional image of a scene including the surface  
{ TAIL ~ The method } comprises illuminating the first object so as to produce a shadow of { HEAD ~ the first object } on a surface lying at a known position with respect to the second object and forming a two dimensional image of a scene including the surface
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD 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 OTH OTH OTH OTH OTH OTH