Using Subgraph Isomorphisms to Recognize and Decompose Boundary Representation Features

Abstract

A method using subgraph isomorphisms is presented for both computer recognition of shape features and feature-based decomposition of a solid from a boundary representation (B-rep). Prior to the recognition process, the face-edge graph of an object is extracted from a B-rep and is labeled by shape elements as a shape graph, which is an abridged B-rep and is labeled by shape elements as a shape graph, which is an abridged B-rep input to the recognition system. A feature is defined by a user as a feature graph, which is conceptualized from a regional surface shape on a valid solid. Feature recognition is achieved by finding a subgraph from the shape graph of a designed object where the subgraph is isomorphic to a feature graph. Because of the high complexity in subgraph matching, a node classification algorithm is used to reduce the search space. Through this recognition process, the surface of a solid can be decomposed into a collection of features according to a library of feature graphs. The feature relationships are represented in a relationship graph considering the features as nodes and their relationships as arcs. This research shows that the definition of features can be user-definable and consist of valid boundary representation elements in the solid world, and that a heuristically fast algorithm can increase the possibility to recognize features in a reasonable time.