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Geometric and Feature modelling

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A feature-based solution to the persistent naming problem

**Abstract**

Current parametric modeling systems suffer from the persistent naming problem, which is responsible for the unpredictable, sometimes stunning, behavior of such systems when re-evaluating a model, even after simple editing operations.

This paper claims that the problem is an inherent difficulty of the approaches taken by current parametric modeling systems, in which various persistent naming schemes end up solving only a fraction of the problem. Instead, it is argued that the rationale behind such schemes should itself be revised. Alternative approaches to define a parametric model based on persistent parametric entities can, in fact, eliminate the flaws of using references to non-persistent geometric model entities, which is the real cause of the problem.

One such approach is described here, which is able to take full advantage of parametric modeling. It provides persistent entities in the parametric definition domain, which can always be consistently referred to. Basically, it proposes the use of the names of persistent feature faces, instead of the names of boundary faces, every time a reference to a face is required in a parametric definition. Furthermore, it makes use of these feature faces names in order to identify any edge of interest on the boundary representation of the model. These edge names can then be consistently referred to in further parametric definitions. Whenever ambiguities occur, e.g. due to multiple intersections, half-spaces are automatically defined by means of references associated to the features involved, which are kept in the parametric domain.

An implementation of this approach is also described, which takes care of maintaining the semantics of the parametric definition of a solid object. A number of examples illustrate how user specification of modeling operations can be transparently performed through interaction with a declarative feature model.

download full paper

Bidarra R, Nyirenda PJ and Bronsvoort WF (2005), A feature-based solution to the persistent naming problem. *Computer-Aided Design and Applications * Vol. 2, no. 1-4, pp. 517-526 (special issue: Proceedings CAD'05, Bangkok, Thailand, 20-24 June)