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From: Christopher Sean Morrison <brlcad@ma...>  20130701 04:36:49

On Jun 28, 2013, at 6:39 AM, Tom Browder wrote: > On Thu, Jun 27, 2013 at 10:06 PM, Clifford Yapp <cliffyapp@...> wrote: >> For anyone interested in the early history of BRLCAD, three reports from >> the 1987 USENIX Computer graphics working group that are (to the best of my >> knowledge) the first presentations in a public forum documenting the BRLCAD >> system are now available online as ARL reprints: > ... > > I notice that all three authors clearly defined CSG as "combinatorial > solid geometry" and not "constructive solid geometry" as some are wont > to say. Our team stopped documenting CSG as "combinatorial solid geometry" now over 10 years ago. "Combinatorial" is the more mathematically based terminology, but the solid modeling community (industry and academia) firmly adopted "constructive" as the understood nomenclature. We still use it from time to time, but there's no intention one way or the other, just habit. I personally never bought into the debate as one can just as well talk about the combinatorial nature of the underlying boolean expressions or how one constructively defines 3D space using boolean expressions. This holds even for intersection and difference operations, so it's just a slight change in perspective of what the term refers to. We continue to be the champions of all things mathematicallybased including being proponents of CSG, but our current and longterm strategy is to focus on hybrid representation capability. Supporting explicit boundary representation (BREP/NURBS) geometry improves our interoperability with other CAD systems tremendously. Eventually, we'll get to the point where parametric feature editing will hide boolean operations and the underlying geometry representation format (implicit vs explicit) will rarely be encountered by the modeler. All geometry will be simultaneously represented in implicit and explicit form for modeling convenience. We're adapting to no longer be strictly a CSG modeling system but, rather, a fully generalized solid modeling system. Cheers! Sean 