Chinese Journal of Computers   Full Text
Title	A B-rep Model Decomposition Approach Based on Face Shell Shrinking
Authors	MA Lu-Jie HUANG Zheng-Dong
Address	(National CAD Support Software Engineering Research Center, Huazhong University of Science and Technology, Wuhan 430074)
Year	2009
Issue	No.6(1183—1195)
Abstract &   Background	Abstract Decomposition of 3D solid models with B-rep format is a crucial problem in transforming the models to CSG format, and it also benefits shape and structure analysis of these models. Here, a face-shell shrinking approach for model decomposition is presented. First, cutting loops of a B-rep model are recognized through local shape analysis, then the B-rep model is decomposed into multiple face shells along edges in the cutting loops, and finally, the face shells are transformed into solids by shrinking the cutting loops on the faces. With the above three steps, B-rep models with quadric surfaces can be effectively decomposed into the composition of positive and negative volumes. At the same time, the experimental results show that this approach is efficient. Keywords B-rep model; model decomposition; cutting loop; face shell; shrinking Background In the area of computer-aided design, decomposition of 3D solid models with B-rep format is a crucial technique for feature recognition, feature conversion, model analysis and transformation. With the wide application of three-dimensional CAD software, 3D solid models increase in a high speed. This implicitly poses a question how to reuse the models. Usually, model reusage is based on model understanding, and model understanding can be achieved through geometrical shape analysis. This paper just presents a model decomposition method to support model shape analysis. Although some approaches have been proposed to solve this problem in the past two decades, the problem hasn’t been resolved effectively. Some approaches are only limited to polyhedron model, while others are difficult to implement. Usually, the time costs of these approaches are high. In addition, the existing methods share a disadvantage that only positive features can be decomposed from solid model while negative features can not. This problem goes against the need of structure analysis of CAD model because most of CAD models both have positive and negative features in structure. The model decomposition method presented in this paper based on a face-shell shrinking can overcome the above problems of existing methods. It can decompose solid models with quadric surfaces into positive and negative features with a high computation efficiency. However, like the other existing methods, the approach proposed in this paper also cannot deal with the solid model with free-form surfaces. This is a difficult problem. It will be conducted research on it in future. The work of this paper has been supported by the two projects from National Natural Science Foundation of China(No.60573178 and No.50875092). The major objective of the first project is to study shape and structure relations of solid models in a large CAD model database, and to discover the useful information through simultaneously analyzing multiple models. The latter project is to study the rationality of design structure in solid models as well as the comparison of the structures. So the contribution of this paper is a basic technique problem to both of the above two projects, and it can support the following research work of the two projects. The authors of this paper have already done research in the area of feature recognition, feature conversion and shape analysis in the past, and some papers have been published in Computer-Aided Design, ASME Journal of Computing and Information Science in Engineering, ASME Journal of Manufacturing Science and Engineering, Journal of CAD & CG and so on.