Issues on feature-based editing and interrogation of solid models

Abstract

Operations that create additive or subtractive volume features, such as bosses or slots, simplify the computer aided design of mechanical parts. Surface features, whether extracted automatically or selected interactively, group functionally related boundary elements, and thus provide an expedient interface between CAD systems and analysis or manufacturing applications. Despite much progress in CAD, design remains an iterative process and involves error-prone modifications of previous solutions. Features should in principle offer a high level vocabulary for characterizing errors and for specifying how they should be corrected. This paper points out the semantic ambiguities of simplistic feature-based commands for editing models. It recommends procedural models for editing volume features, and corrective volumes for editing surface features. It shows how space decomposition techniques and CSG expressions based on active zones reduce the cost of executing an editing command. Error detection may be automated by supporting intentional features, which correspond to the desired characteristics of the model, and by endowing them with domain dependent validity criteria expressed in terms of associated geometric elements. The paper demonstrates that validity may be tested by simply interrogating a mixed-dimensional geometric structure which is used to represent not only the model, but also the interactions between the geometric elements associated with intentional features.