An extended Gaussian image (EGI) is constructed by mapping the surface normals of an object onto the Gussian sphere. The attitude of an object is greatly constrained by the global distribution of EGI mass over the visible Gaussian hemisphere. Constraints on the viewer direction are derived from the position of the EGI mass center, and from the direction of the EGI inertia axis. The algorithm embodying these constraints and the EGI mass distribution are implemented using a lookup table. A function for matching an observed EGI with the prototypical EGIs is also proposed. The algorithm determines the attitude of an object successfully both from a synthesized needle map and a real needle map.
