Polygonal object recognition

A technique for recognizing a 2-D unoccluded polygonal object by combining the alignment method with efficient string matching algorithms is presented. The approach is based on a single anchor point: the gravitation center of the contour of the object (GCC). The GCC is stable and insensitive to digitization errors, and it can always be found and calculated very efficiently. Additionally, it is universal and does not depend on the specific library of known objects. In this approach, most of the work is done in the preprocessing stage, when all of the library objects are transformed into a GCC canonical representation form. For the recognition stage, the canonical representation of the unknown object concatenated to itself is considered as a 'text' and the canonical representation of the known library objects as a set of 'words.' The recognition problem is then reduced to finding all of the occurrences of the 'words' in the 'text,' for which an efficient O(n) algorithm is introduced, where n is the order of the polygon being recognized. This approach was evaluated with several sets of objects from different fields, and very satisfactory results were obtained.