Boundary evaluation using inner and outer sets: the ISOS method

A boundary-evaluation algorithm for constructive solid geometry is presented for representations in which the primitives can be bounded by complex surfaces (such as splines) as well as by simpler polynomial surfaces. A fundamental part of the algorithm is the spatial decomposition of each primitive in a way that yields three planar bounded volumes, one containing the primitive (outer set), one contained within the primitive (inner set), and the third being the set difference of the first two, containing the boundary of the primitive. A positive feature of this approach is that the geometric coverage can be extended to any family of solid primitives for which an initial inner-solid-outer-solid segmentation and a subdivision procedure can be devices. Satisfying these two requirements ensures that the resulting primitive definitions are in the canonical form necessary for evaluation. Therefore the cost in terms of software development of adding primitive types does not depend on the number or type of existing primitives.<>