Modelling with constraints: Theoretical foundation and application

Modelling with constraints is a modem approach to product modelling. Engineering knowledge is associated with geometry and topology in the product model. Together with the technique of feature based modelling, modelling with constraints has widely affected the development of new CAD-systems. The architecture of so called parametric CAD-systems reflects the impact of these new technologies. Besides the new hybrid modellers of geometry and topology, the sketcher and the constraint solver have become key components in a parametric CAD-system. The sketcher may be regarded as a designer interface for modelling with constraints. Moreover rule-based methods of automatic constraint detection are applied in sketchers. Constraint solvers evaluate the network of constraints formulated by the sketcher as a set of equations or predicates using numeric or symbolic algorithms or rule based approaches. The article closes with a summary of the advantages and risks of designing with constraints, showing typical application fields of this modelling technique and discussing some open issues.