Résumé
CAD assemblies are essentially reduced to a set of components, often solids, and a user-defined tree structure. Given the generation process of CAD assembly models where the user may instantiate several times a given component, some solids may occur more than once. If this tree structure incorporates some functional information, this is not mandatory and it cannot be regarded as a reliable functional description. Similarly, component occurrences may not always end up being simple copies of a given solid. To this end, we introduce the concept of intrinsic assembly model and describe and illustrate an associated set of geometry processing operators that can produce an intrinsic shape descriptor of assembly components and extract assembly structure using symmetries, alignments, ... As a complement, it is described how this intrinsic model can become an intrinsic knowledge-based assembly model. Some geometric concepts are mapped to symbolic information using ontology and new structural assembly information is derived using inferences. All these automated processes and mappings enforce the consistency of the proposed model. Illustrative examples show that this model is a first basis toward a functional description of an assembly where new inference rules can be added to express and characterize functional information. A website
http://3dassblyanlysis.gforge.inria.fr/3d/
gives a public access to a knowledge-based assembly example (available with IE and Firefox navigators).