A Reconfigurable 3d Engineering Shape Search System Part Ii: Database Indexing, Retrieval and Clustering

The paper introduces database and related techniques for a reconfigurable, intelligent 3D engineering shape search system, which retrieves similar 3D models based on their shape content. Feature vectors, which are numeric “fingerprints” of 3D models, and skeletal graphs, which are the “minimal representations of the major shape” of a 3D model, represent the shape content. The Euclidean distance of the feature vectors, as well as the distance between skeletal graphs, provides indirect measures of shape similarity between the 3D models. Critical database issues regarding 3D shape search systems are discussed: (a) Database indexing, (b) Semantic Gap, (c) Subjectivity of similarity, and (d) Database clustering. An R-tree based multidimensional index is used to speed up the feature-vector based search operation, while a decision treebased approach is used for efficiently indexing/searching skeletal graphs. Interactions between users and the search system, such as relevance feedback and feature vector reconfiguration are used to bridge the semantic gap and to customize the system for different users. Database clustering of the R-tree index is compared with that generated by a selforganizing map (SOM). Synthetic databases and real 3D model databases were employed to investigate the efficiency of the multidimensional index and the effectiveness of relevance feedback.