Virtual Reality (VR) technology is a natural extension of 3D computer graphics with advanced input and output devices and brings a completely new environment to the CAD community. However, with today’s VR systems, it is difficult to directly and precisely create and modify objects in a VR environment. This paper presents an efficient approach for solid modelling in a VR environment. Solid modelling in the VR environment is precisely performed in an intuitive manner through precise constraint-based manipulations. Constraint-based manipulations are accompanied with automatic constraint recognition and precise constraint satisfaction for establishing the hierarchically structured constraint-based data model and are realized by allowable motions for precise 3D interactions in the VR environment. The allowable motions are represented as a mathematical matrix for conveniently deriving the allowable motions from constraints. A procedure-based degree-of-freedom incorporation method for 3D constraint solving is presented for deriving the allowable motions. A rule-based constraint recognition engine is developed for automatic constraint recognition. A prototype system has been developed for solid modelling in the VR environment, where the user can create solid models in an intuitive manner through precise constraint-based manipulations.

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