| Computer-Aided Design and Computer-Aided Manufacturing(CAD/CAM) are important parts of the advanced manufacturing technology. With the development of the computer network, collaboration has become a trend of CAD/CAM technology, and more and more research work has been done on collaborative CAD/CAM system.A web-based collaborative CAD/CAM system, C-Superman, has been developed by the Research Center of CAD/CAM Engineering of Nanjing University of Aeronautics and Astronautics. The C-Superman system has the functions of collaborative geometric modeling, NC programming and so on. On the basis of C-Superman, geometric editting and improved displaying technologies of geometric models are studied and the following achievements have been accomplished.1. The collaborative geometric modeling of C-Superman is based on Java3D and ACIS, and geometric editting is an important part of the geometric modeling. Taking advantage of the incremental facetting, this paper facets the ACIS model on the server, so that computational time and the data transmission quatity through network are reduced, and quick display of the client model has been realized.2. A method is introduced to construct the Level-of-Detail(LOD) model. The geometric modeling of the C-Superman system is based on the ACIS modeler. Aiming at the defects of the ACIS mesh models, a mesh simplification algrithom is introduced, which is based on the criteria of the angle between the normals of two triangular facets. Through twice simplification to the original model, a three-level LOD model is obtained.3. The LOD model is a complex data structure, therefore how to transmit model data efficiently between the client and the server is an important work. The vertices'coordinates are transmitted only once, and the different models are represented by the vertices'index whose data volume is much smaller than the vertices'coordinates, so the data volume to be transmitted is reduced remarkably. |
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