are defined by lines, conics, polylines, surface curves, or b spline curves ISO 10303-514 Advanced boundary representation, a solid defining a volume with possible voids that is composed by advanced faces ISO 10303-509 Manifold surface, a non intersecting area in 3D that is composed by advanced faces ISO 10303-521 Manifold subsurface, a sub-area out of a manifold surface ISO 10303-508 Non-manifold surface, any kind of advanced face arrangement ISO 10303-513 Elementary boundary representation similar to ISO 10303-514, but restricted to the elementary surfaces only ISO 10303-512 Faceted boundary representation a simplified surface model constructed by planar surfaces only See also B-spline Bezier curve Bezier surface Combinatorial maps Constructive solid geometry (CSG) Coons surface Function representation Geometric modeling kernel NURBS Solid modeling Spline Winged edge Further reading Further information about Boundary Representation can be found in a variety of papers and the following books: External links OpenCascade - an open source library for BRep solid modeling Actual example of source boundary representation in STEP format SimpleGeo - a B-rep/CSG hybrid modeling system for Monte Carlo particle transport simulations FreeREP - Opensource geometry kernel development Brep - A boundary representation based modeler Computer 3D graphics