Method and apparatus for locating and decoding machine-readable symbols

In a computer system having a processor and a data storage device, a computer implemented method of locating a predetermined pattern of convexly curved shapes and spaces between the convexly curved shapes within an image stored in the data storage device, the convexly curved shapes at least partially surrounding a preselected point, the method comprising the steps of:

• locating all curved shapes within the stored image, including the convexly curved shapes of the predetermined pattern;
• determining a pair of tangent lines from endpoints of each located curved shape;
• defining a line between each pair of tangent lines;
• determining at least one point of intersection of the defined lines;
• and
• locating the preselected point based on the at least one point of intersection of the defined lines.

An apparatus for decoding a machine-readable symbol representing encoded information, the machine-readable symbol including a plurality of spaced two-dimensional shapes, the symbol having a predetermined orientation pattern of convexly curved shapes and spaces between the convexly curved shapes, the convexly curved shapes at least partially surrounding a predetermined point of the symbol, the apparatus comprising:

• a sensor that receives light that is reflected from the symbol and produces an output signal therefrom that represents the reflectance of the shapes and spaces comprising the symbol;
• a receiver that receives the output signal and produces a digital signal representing an image of the shapes and spaces of the symbol;
• a storage device for storing the digital signal;
• and
• a processor for processing the digital signal and producing a signal indicative of the information encoded in the symbol, the processor (a) locating all curved shapes within the stored digital signal, (b) determining a pair of tangent lines from endpoints of each located curved shape, (c) defining a line between each pair of tangent lines, (d) determining at least one point of intersection of the defined lines, (e) locating the predetermined point based on the at least one point of intersection of the defined lines, and (f) decoding the symbol and producing a signal indicative of the information encoded in the symbol based on the located predetermined point of the symbol.