Patent ID: 7834728

Claim:
A method for producing a two dimensional code, said method comprising the steps of: a. selecting a 1×n code having desired correlation characteristics, said 1×n code having n code elements CE i , where i=1 to n; b. producing, using said 1×n code, n rows R i , where i=1 to n; and c. combining the n rows into an n×n matrix of n columns and n rows to produce an n×n code corresponding to a spatial force function when said n×n code is used to define a plurality of field emission sources of a first field emission structure having a first orientation relative to a second field emission structure said n×n code corresponding to a code modulo of said first field emission structure and a code modulo of said second field emission structure, said n×n code defining a peak spatial force corresponding to substantial alignment of said code modulo of said first field emission structure with said code modulo of said second field emission structure, said n×n code also defining a plurality of off peak spatial forces corresponding to a plurality of different misalignments of said code modulo of said first field emission structure and said code modulo of said second field emission structure, said plurality of off peak spatial forces having a largest off peak spatial force, said largest off peak spatial force being less than half of said peak spatial force.