On 6/9/07, Ken Elliott <kelliott11@cfl.rr.com> wrote:
> Ken Elliott wrote:
> > Compare the Stealth Figher vs. the B2 Stealth Bommer.
>
> Chuck Hast wrote:
> > The flat surfaces on the stealth fighter are set in such a way
> > as to scatter radar and reduce the reflectivity of the fighter,
> > that is why it is like that not due to the design limitations.
>
> I suggested this example because BOTH are designed to scatter radar. But
> the flat surfaces tend to create a more focused reflection than the
> non-uniform curved surfaces of the B2 Bommer. The figher has flat surfaces
> because of the limitations of the CSG modeler and lack of processor power.
> This is well known among CAD developers.
>
> CSG modelers usually describe non-uniform curved surfaces as a series of
> connected triangles. The smoother the surface, the more triangles. Trying
> to model a water hose can take millions (or more) of triangles, while a
> NURBS modeler only needs 2 entities: a cross section curve (like a circle)
> and a path curve. NURBS curves are very lightweight in data, but it takes
> lots of number crunching to process it.
>
> In the past, NURBS were not practical for simple geometry (tables, houses,
> tanks) because of the overhead of caluculations. CSG is super fast, and as
> long as the geometry didn't get too complex, it was the tool of choice.
> Most CAD systems today started off as CSG modelers. But once the CPUs got
> fast, NURBS became possible, then practical, and now there is little reason
> not to use them. This development occurred in the late 90's, and the first
> affordable modeler (under $30,000) appeared on the market (Rhino in 98, I
> think).
>
> So here's the big deal about Rhino. All other CAD packages started off as
> CSG, and added some NURBS entities. So your model is a mixture of CSG and
> NURBS. Rhino is 100% NURBS, except for text and dimensions. It can simply
> do things that no other modeler can do. Just having this package on Linux
> would be a wonderful thing. But McNeel has opened the source code and specs
> of the file format. No other CAD company does this - they all hold your
> design data hostage. McNeel is by far the most open minded of all the CAD
> vendors. The tool is fantastic and he thinks like open source people think.
>
> OpenNURBS greatly lowers the difficulty of bring high-end design tools to
> Linux, and we badly need this sort of thing for Linux to be taken serious in
> engineering circles. Here's a thermal analysis program that supports Linux.
> http://www2.rhino3d.com/resources/display.asp?language=en&listing=107
>
> This is all good for Linux. Engineering and design tools were one of the
> early target markets Microsoft went after with Windows NT. The field was
> dominated by Unix workstations, and MS went after them with a lower cost
> platform. If anyone in a large company will be pro-Linux, it would be IT
> people first, then engineers. I watched MS work hard to woo the CAD
> developers in the early 90's and it paid off big time.
>
> Vote here:
> http://offbroadway.blogspot.com/
>
> OpenNURBS
> http://opennurbs.org/
>
> CSG
> http://en.wikipedia.org/wiki/Constructive_solid_geometry
>
> NURBS
> http://en.wikipedia.org/wiki/NURBS
>
> I'll shut up about this for now. As you can tell, I'm passionate about
> getting good engineering tools ported to Linux.
>
> Ken Elliott
>
> =====================
> -----Original Message-----
> From: slug@nks.net [mailto:slug@nks.net] On Behalf Of Chuck Hast
> Sent: Friday, June 08, 2007 2:25 PM
> To: slug@nks.net
> Subject: Re: [SLUG] Real World Class 3D modeler for Linux
>
> On 6/8/07, Ken Elliott <kelliott11@cfl.rr.com> wrote:
> > >> If you can design tanks with it you can design anything with it.
> >
> > Far from it. Tanks are simple geometry. Streight edges, flat sides, etc.
> > Items with smooth curved surfaces are much more difficult. Think car
> > bodies, boats, consumer goods.
> >
> > Compare the Stealth Figher vs. the B2 Stealth Bommer. The figher is
> > all flat sides due to the limitations of the software and cpu
> > horsepower used at the time. NURBS and fast computers allowed for the
> > complex calculations required for a complex curved surfaces.
> >
> > But if you disagree, that's fine. I've only been using CAD systems
> > for 25 years and I could be wrong...
> >
>
> The flat surfaces on the stealth fighter are set in such a way as to scatter
> radar and reduce the reflectivity of the fighter, that is why it is like
> that not due to the design limitations. It is all about radar signatures and
> those flat faces are set in such a way to make it hard to get a good primary
> return off of the aircraft.
>
> --
> Chuck Hast -- KP4DJT --
> To paraphrase my flight instructor;
> "the only dumb question is the one you DID NOT ask resulting in my going out
> and having to identify your bits and pieces in the midst of torn and twisted
> metal."
> -----------------------------------------------------------------------
Not at all. The info is much appreciated. As I mentioned before,
I've been on the lookout for such. Passion is important as it drives
one to learn more and more about a complex piece of software.
Obviously it must be something amazing to impress your experience
level. I'm eager to compare it with SolidWorks. I'm keeping a copy
of this thread to aid me.
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