A cell-based approach for generating solid objects from orthographic projections

Abstract

This paper describes an efficient method for converting orthographic projections into solid models based on non-manifold topology and the assumption-based truth maintenance system (ATMS), and then describes an error recovery method for incorrect orthographic projections. A combination of non-manifold modelling and ATMS achieves excellent performance for conversion problems. In our method, all solid candidates are maintained by a cellular model using non-manifold topology. Since a combination of cells in a cellular model determines the shape of a solid, solid models that match orthographic projections can be derived by solving constraints between cells and orthographic projections. A sufficient group of constraints can be expressed as a set of Boolean equations, which can be solved efficiently by using ATMS. Our method can even be applied to incorrect draftings. In actual design, many draftings contain human errors, but conventional methods cannot handle such incorrect draftings. We discuss methods for detecting inconsistent lines that should not have been included, or missing lines that should have been included. © 1997 Elsevier Science Ltd. All rights reserved.