A VR-CAD Data Model for Immersive Design
Résumé
This work focuses on direct and interactive modifications of CAD objects in Virtual Reality (VR). Usually, CAD software requires some skills (experience and knowledge), on its functionalities and representations, as well as on the design history of CAD objects. On the other side, VR brings new paradigms for 3D interaction, and one needs intelligent middleware to manage CAD objects in any immersive Virtual Environment (VE). Previous work proposed a mechanism allowing implicit edition of the Construction History Graph (CHG) of CAD objects, based on the direct manipulation of their 3D visual representations. A labelling technique of the Boundary Representations (B-Rep) elements, coupled with an inference engine, provided a backward chaining of B-Rep elements towards the operators of a customized CHG. In this paper we propose a generalization of this approach to apply it to any CAD system based on B-Rep and CHG models. Firstly, several encapsulations structures are defined, to manage CHG nodes as well as the B-Rep components. Secondly the labelling, now attached to the encapsulations of the B-Rep elements, has been extended to a multi-labelling. This solves the issue of the B-Rep elements which are the result of several CHG operators, and more generally allows that several parameterizations of a CAD object may be proposed for its shape modification, when selecting any B-Rep element. These improvements make it possible direct and interactive modifications of CAD objects previously designed, by parsing native CHG of a given CAD system, to fill our structures with useful data for their 3D edition during a VR session. Moreover the multi-labelling mechanism grants the manipulation of CAD objects to non-experts through the inference engine. As a proof of concept we present cRea-VR, our VR-CAD model applied to CATIA.