Abstract

Nef polyhedra in d-dimensional space are the closure of half-spaces under boolean set operations. In consequence, they can represent non-manifold situations, open and closed sets, mixed-dimensional complexes, and they are closed under all boolean and topological operations, such as complement and boundary. They were introduced by W. Nef in his seminal 1978 book on polyhedra. The generality of Nef complexes is essential for some applications. In this paper, we present a new data structure for the boundary representation of threedimensional Nef polyhedra and efficient algorithms for boolean operations. We use exact arithmetic to avoid well known problems with floating-point arithmetic and handle all degeneracies. Furthermore, we present important optimizations for the algorithms, and evaluate this optimized implementation with extensive experiments. The experiments supplement the theoretical runtime analysis and illustrate the effectiveness of our optimizations. We compare our implementation with the ACIS CAD kernel. ACIS is mostly faster, by a factor up to six. There are examples on which ACIS fails. The implementation was released as Open Source in the Computational Geometry Algorithm Library (CGAL) release 3.1 in December 2004.

Citations