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