Method for finding holes and pockets that connect multiple faces in 2 1/2D objects

Given a boundary representation, the problem of identifying sets of faces that bound holes and pockets in 2 1/2D objects is relatively trivial when they emanate from a single face, because the edges of the depression form an inner loop of convex edges. There are, however, many components in which a hole or pocket is present, and yet defines no inner loop on any face; in other words, it has a nonunique entrance face. The paper describes an algorithm, based on the manipulation of a face-edge graph, for identifying sets of faces in a 2 1/2D object that bound holes or pockets with unique or nonunique entrance faces. The algorithm also determines the perimeter of the projected area enclosed by each hole or pocket in a specific direction. This information is of direct use in the manufacture of the component. © 1991.