Accelerating the evaluation of volumetric modelers by manipulating CSG trees and DAGs

Abstract

A CSG-based interface is commonly used in CAD systems as the main technique for defining objects. The CSG definition (trees or dags) is used regardless of the internal representation scheme, and it is particularly popular with volumetric geometric modelers (e.g. octree-encoding and switching-function based representation). The resources required to generate the volumetric code depend on the specific CSG definition, which may contain operations that are expensive to perform with the volumetric representation. As the CSG definition is not unique, it can be manipulated to obtain an equivalent CSG definition that is more suitable for generating the volumetric code. The paper presents methods that eliminate costly operations from the internal nodes of a CSG definition, and transfer them to the level of the leaves (where they are not expensive to perform), before the volumetric code is generated. A consequent reduction is achieved in the resources required to generate the volumetric code.