A process for decoding coded data is provided. The coded data has a plurality of layouts which each have order n (at least two) rotational symmetry and encode a codeword of a sequence of n symbols distributed at n locations about a center of rotational symmetry of the respective layout such that decoding the symbols at each of the n orientations of the layout produces n representations of the codeword. Each representation is a different cyclic shift of the codeword and is indicative of the degree of rotation of the layout. The process involves, at the computer system, identifying a layout from an image including the coded data, decoding the identified layout to determine a codeword representation, and determining a degree of rotation of the layout from the determined representation.