DEPTH-ORDER POINT CLASSIFICATION TECHNIQUES FOR CSG DISPLAY ALGORITHMS

Constructive Solid Geometry (CSG) defines objects as Boolean combinations (CSG trees) of primitive solids. To display such objects, one must classify points on the surfaces of the primitive solids with respect to the resulting composite object, to test whether these points lie on the boundary of the composite object or not. Although the point classification is trivial compared to the surface classification (i.e., the computation of the portion of the faces of primitive solids that lie on the boundary of the composite object), for CSG models with a large number of primitive solids (large CSG trees), the point classification may still consume a considerable fraction of the total processing time. This paper presents an overview of existing and new efficiency-improving techniques for classifying points in depth order. The different techniques are compared through experiments.