Extracting geometric features from a virtual environment

In the fields of computer aided design (CAD) and virtual reality (VR), ther e have been various approaches in converting geometric models from a CAD en vironment to a VR environment for virtual prototyping purposes. Comparative ly, little work has been published on the inverse modelling issues from VR to CAD. Robust algorithms on inverse modelling will facilitate model updati ng if an object is directly modified in a virtual environment (VE). This pa per presents algorithms for constructing a high-level CAD model from a poly gonal model found in a virtual environment. The faceted model is first unif ormly sliced in three-orthogonal directions and a contour-based surface mod el is created. Boundary points are then identified from the contour model. A network of boundary curves is further constructed with the vertices of th e neighboring polygons of the original VR model derived from the previously identified boundary points. The boundary curves partition the entire surfa ce of the object into individual surface areas and form the topology of the object. The type of an individual surface is further identified. A concise surface description is then reconstructed for each of the surface areas fr om the corresponding vertices falling inside the topological domain. Some e xamples are presented to illustrate the developed algorithms. (C) 2000 Else vier Science B.V. All rights reserved.