Constraint-based feature validation
PhD student - Maurice Dohmen |
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A constraint-based feature validation scheme has been developed that provides the means to specify and maintain the validity of features in multiple views. For feature validity specification, various constraint types of different domains have been identified: geometric, algebraic and topologic. A scheme for persistent feature validity maintenance has been developed, which is based on constraint management.
The constraint management is separated into two levels: constraint storage and constraint satisfaction. Firstly, the constraint management module maintains in a constraint graph the set of constraints that result from modelling actions. Secondly, it ensures satisfaction of all constraints by deploying several constraint solvers that are each specialized for a particular domain. The module maintains a coupling between the two levels, and it propagates solving results between the constraint solvers. The advantages of the two-level separation are that the interdependence of the constraints is handled by the constraint management module, while the constraints are satisfied efficiently by the solvers.
A geometric constraint solver has been developed based on extended 3D degrees of freedom analysis. Newly developed extensions include degrees of freedom ignorance for locus intersections, and restructuring of constraint loops. With these extensions, powerful 3D geometric constraint solving is achieved. For the analysis of over- and underconstrained geometric models, the concept of dependency graph has been developed, to identify the set of involved constraints.
Algebraic constraint solving is done with the SkyBlue solver; its constraint priority scheme is used to propagate feature parameter changes in such a way that the model is minimally disturbed.
Topologic constraints are checked by querying a cellular geometry representation; it allows detection of violations of topologic feature properties caused by feature interactions.
Product modifications are propagated between the views by link constraints that provide a generic coupling of the feature models of the views. A view priority scheme is used to handle conflicts between constraints of different views.