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.
>
I too, my biggest issue still remains with mapping. I do a lot of mapping
and end up going to windows stuff because I just can not get what I need
out of the stuff I find for Linux unless I am willing to shell out the big bux
and get something I can not afford.
It is a real shame, most all of this art started out on some form of Unix
work stations as you pointed out, but the providers forgot their roots. That
is sad.
-- 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." ----------------------------------------------------------------------- This list is provided as an unmoderated internet service by Networked Knowledge Systems (NKS). Views and opinions expressed in messages posted are those of the author and do not necessarily reflect the official policy or position of NKS or any of its employees.
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