{HEAD ~ The method} comprises illuminating {TAIL ~ the first object} so as to produce a shadow of 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  
comprises illuminating
{ HEAD ~ The method } comprises illuminating { TAIL ~ the first object } so as to produce a shadow of 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
HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL 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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH