An article includes a substrate with a physical surface, and a hierarchy of parent and child optical element sets embodied on the physical surface, such that a first encoded value represented by the parent optical element set is based at least in part on the visual appearance of a particular optical element in the child optical element set, and a second, different encoded value represented by the particular parent optical element is based at least in part on the visual appearance, and the second encoded value not being decodable from a distance greater than a threshold distance, the first encoded value being decodable from the distance greater than the threshold distance.