Topology based tolerancing for geometric modeling operations

摘要

The invention relates to a method and apparatus for tracking and modifying the accumulated error and the current operational tolerance of each topological entity in a geometric model of a three dimensional object. Each topological entity has assigned to it a Mintol value and a Maxtol value, Mintol represents the current accumulated error associated with the entity. Maxtol represents the operational tolerance of the entity for future operations. The Mintol value for an entity is set and occasionally adjusted so that it comprises a volume which encompasses all other entities adjacent to the particular entity. With respect to Maxtol, when two entities are within a distance from each other which is less than the sum of the Maxtols of the two entities, the two entities can be combined. Maxtol is adjusted whenever Mintol is adjusted so as to remain larger than Mintol and whenever a new entity is created by the combination of old entities, so as to encompass the Maxtols of the two old entities.