Point-based persistent identification of transition features for parametric CAD data exchange

Abstract

TransCAD is a specialized CAD system for data exchange that is based on a set of standard modeling commands through which the macro file of a CAD model is exchanged. A problem in CAD data exchange has been the consistency of persistent identifiers among different commercial CAD systems. Identifiers serve the purpose of unique and unambiguous naming for topological entities. The current identification approach experiences problems that are caused due to its topology-based mechanism. These problems of TransCAD lead to wrong translation of simple transition features (constant radius fillet/chamfer) between commercial CAD systems. Outside TransCAD, different commercial features-based translators were surveyed to check their status. These translators face issues in the exchange of advanced transition features (variable radius fillet). These problems result from a mismatch of reference points used to define advanced transition features. Currently, neither TransCAD nor commercial feature-based translators can correctly translate these features. An identification approach based on a point that has both geometry and topology information is proposed. The names of topological entities i.e. face, edge, and vertex are based on the names of their adjacent points. A point-based name is optimized to have most of the data needed for the mapping of arguments used in entity selection commands. This point-oriented naming method is implemented and verified in TransCAD. The proposed method is then used in the development of translators for exchanging problematic test models. It can be extended to other unsupported features as well as assembly models in TransCAD.