Disadvantages:

• Shapes described with this representation seem to be far more difficult for a person to reconstruct than with the ASSF representation. Although the representation made it easier for a computer program to reason about object interaction, it is not necessarily a good representation for people to deal with (as would be necessary in robot programming).
• Description of the relative position of objects only in terms of boundary elements made it difficult to reason about relative motion of objects. Most motion operations extrapolated from an element position to produce a derived object orientation, and then used this description for reasoning with. It may have been more appropriate to include object-scale orientation explicitly.
• Direction is represented very imprecisely, and the relative directions of boundary segments on opposite sides of an object may be completely unknown, because of the cumulative effects of unknown angles around the boundary between them.

Overall, the extended polygon boundary representation is simpler than the ASSF representation, and it appears to offer more power for reasoning about interaction between objects in two dimensions. The main reason for this is that important factors in object interaction are explicit in the EPB/PDO representation. These factors include the representation of the boundary itself, where interaction takes place, and of the relationships between boundary elements on different objects, which can be used to identify possible interactions.