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 {TAIL ~ a scene} including the surface  
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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 { TAIL ~ a scene } including the surface
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