Research On Key Issues In Network-Centric Geometric Modeling

The development of CAD/CAM and internet techniques has changed the way the product design and manufacturing is working. Globalization of design and manufacturing activities becomes prevalent, which led to a new field called network-centric geometric modeling, and multi-resolution modeling, model sharing and security in a collaborative environment are the three most important techniques in network-centric geometric modeling. The thesis intends to do research on the theory and application of these three techniques. The thesis introduces the history of the development of geometric modeling with a focus on feature-based modeling technologies. Then related research on multi-resolution modeling, model transmission, sharing and security in a collaborative environment are surveyed.Existing multi-resolution simplification methods are mainly developed for polygonal meshes, which don't fit well in CAD/CAM applications. In this thesis, a new method for multi-resolution modeling of feature-based CAD models has been proposed. The new method is based on the observation that in a feature-based CAD modeler with history dependences, different sets of design features can result in different level-of-details (LOD) of the CAD model. Since children features are depend on their parent features, all children features will be suppressed automatically when suppressing a parent feature. This means that we cannot suppress a feature alone without affecting other features. To solve this problem, we propose in this thesis a De-dependence Feature Suppressing operation in order to suppress a feature alone for various LODs of feature models, together with a scheme for topology entity replacement. A mixed type of LOD criterion is defined to sort different types of features with different priorities in sorting the features.To verify the feasibility and effectiveness of the new method, an integrated prototype system has been developed. The implementation details for multi-resolution modeling of parts and assemblies are presented. Key algorithms are presented in details, including feature sorting, de-dependence feature suppressing, series simplification, refinement of simplified parts and assemblies. Techniques for sketch simplification which is basis of many feature creations are also introduced. Sketch simplification can further simplify the feature model by removing unwanted details resulted from small sketch segments which can't be removed by feature suppressing. A post repairing operation is performed to validity the model.Compared with existing multi-resolution methods, the new method for feature-based CAD models can produce more intuitive results that are much closer to designer's intents. Since only...