Parallel Analysis of Non Convex Shapes Digitized on the Hexagonal Grid

the souare mid case. Two pmllcl algorithms for convex polygonal covering of shapes di~itized on the hexsgonal grid are presented. Both algorithms requise operations having a locat suppnn of a 6-pixel neighhot~rhood. The f i s t algorithm computes a polygon with at most s i x sides, oriented along the six principal directions in the hexagonal grid. Thc second algorithm computes a nearly convex polygon, which fits the shape clorcly. The latter algorithm is less sensitive to pattern rotation and is thus more suited to pnctical appliwt~ons. The concavity regions ate obtained by computing thc difFerence ktween the covering polygon and the shape itself. A concavity tree can rhcn be bu~lt, by iteratively applying the polygonal covering algorithm to the concavity regions ~hemselves. The n d e s of the concavity m c cnn k I:~hcllcd with pnramerers. rc1:ited to geometrical feamtts of the corrcsponding regions. Thc concavity tree is a useful fool For automatic visual inspection. I t can also he used for identifying shapes.