A region defined in relation to a surface, and a method for defining such a region; coded data being disposed within the region, the coded data being indicative of an identity of the region and of a plurality of points within the region; in one embodiment, the coded data comprising a plurality of tags,...http://www.google.ca/patents/US6843420?utm_source=gb-gplus-sharePatent US6843420 - Identity-coded surface with reference points and coded marks
