Method and apparatus for decoding two-dimensional symbols in the spatial

Abstract

A method and system for decoding a two-dimensional optical symbol in the spatial domain. The system determines the orientation of an imaged symbol in the spatial domain by using a template to derive a correlation coefficient between radially adjacent signals at a given angle of the template and comparing the correlation coefficients as the template is rotated with respect to the image. The angle of the highest correlation coefficient corresponds to the orientation of a set of symbol axes which include contiguous elements whose centers are collinear. The system then locates each individual information-encoded element of the symbol by using segments of the symbol defined by the axes, first adjusting for each segment the axis position and element size for subsequent determination of the location of all elements for decoding. The system is disclosed as applied to a symbol constructed as a matrix of hexagonal information-encoding elements arranged in a square, with, at its center, an acquisition target consisting of six concentric rings of alternating light and dark reflectivity.