Research For Interface Technique Of Three-dimensional CAD

The data exchange between 3D-CAD systems is an important component of a CAD system, at the same time, it is a difficulty. The data exchange concerns the data share among different CAD systems; it also has significance to the application and popularizing of home 3D-CAD system. So the research to data exchange between 3D-CAD systems has important applied value. Therefore, a data exchange technique based on B-Rep is proposed in this dissertation, and then several key issues of the technique are studied. In order to solve the problem that the surface is expressed incompatibly, the technique for surface approximating needs to be studied. An algorithm, which combines surface interpolation algorithm and surface approximating algorithm, is proposed. A surface is created by interpolating original points, after more sampled points on the original surface is colleted, an optimized model is built, which is based on the approximating error between the created surface and the new sampled points. Then, the approximated surface is got. For solving the problem that the data precision is different in different 3D-CAD systems, the technique for surface extending is needed, Based on the unclamping algorithm for B-spline curves, an algorithm for extend B-spline surfaces that extrapolates using the recurrence property of the de Boor algorithm, is proposed. With the algorithm, the surface is extended to a give curve with the original part of the surface unchanged. Thus the gap between the face and the edge can be made up. In order to solve the problem that the model's topology is expressed incompatibly, topology reconstruction is needed and topology consistency must be maintained. A relationship between the two systems'topology is established corresponding one to one to reconstruct the topolgy, by adding an edge to the loop properly, the model's topology is reconstructed exactly. On the base of the above research, a data exchange interface program between Parasolid and GEMS is developed with VC++ 6.0, and embedded into 3D-CAD system—GEMS, which is supported by National 863 Project.(Grant NO. 2003AA4Z3110). The interface program works well.