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In order to process caps successfully and to determine the correct extent of an entity-entity blend sequence, it is necessary to distinguish side caps (which do not define the end of the sequence) from end caps (which do). The algorithms for doing this rely on the fact that the end points of any caps will lie on the boundaries of the underlying blended entities. If this does not hold for any particular situation, then the cap may be identified incorrectly. Even if these stipulations do hold, but the number of body edges involved between the start and end points of the cap is large (typically around half a dozen or more), then the cap may be identified incorrectly. Periodic blend surfaces pose a problem since end and side caps may be particularly difficult to distinguish. It may sometimes be apparent that a cap has been identified incorrectly if an error message mentions a particular kind of cap (end or side) when the other type is actually desired.
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