Region delimited coded data having unique length digital signature

摘要

Coded data for disposal on or in a surface is delimited into a number of regions. The coded data encodes an identity of the region in which the coded data is disposed, and a signature formed from at least part of the identity of the region and a substantially random number. The coded data is arranged in accordance with a layout having n-fold rotational symmetry, where n is at least two. The layout including n sub-layouts rotated 1/n revolutions apart about a centre of rotation, at least one sub-layout including rotation-indicating data that distinguishes that sub-layout from other sub-layouts. The random number serves as a padding to pad out the identity to a length unique to the identity.