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." ----------------------------------------------------------------------- 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.----------------------------------------------------------------------- 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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