The method comprises illuminating 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 {HEAD ~ a two dimensional image} of a scene including {TAIL ~ the surface}  
including
The method comprises illuminating 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 { HEAD ~ a two dimensional image } of a scene including { TAIL ~ the surface }
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