Re: VRML instead of STL

Date: Fri Jan 05 1996 - 00:43:43 EET

Paul L. Finelt wrote:
> I continue to wonder why any one would want to work with polygons in an RP
> machine. They represent a degradation of the original surface(s) and often
> times create those problems you mentioned in your opening message.

Unfortunately, present scanners only work with straight lines. Furthermore,
slicing planes is much easier and faster than slicing complex surfaces.
This is basically the two reasons why the surfaces are tessellated
before processing in an RP machine.

Several researchers have developed algorithms to work directly with
CAD models. We had several papers on the subject (see our site).
Unfortunately, even when slicing complex nurbs surfaces and generating
NURBS curves, we still have to segment the curves to communicate with
an RP machine.
Until scanners are developed that follow curves, we ill have to resort to some
segmentation or tessellation.

> If one was concerned with dimensional tolerances, you would try to use
> something like an SLC file where slice data already exists. I realize this
> poses it's own set of problems and limitations. Everthing is going to be a
> trade-off based upon the result desired.
> I still don't understand why you would want to use VRML for Rapid
> Prototyping? It was designed for virtual environments that just have to "look
> good", not parts that have to fit and feel good.

I challenge you to bring us a file (STL) before you build it, and let us show
you what you can do with a virtual model before building a physical model.

> I certainly don't think the chaps who put together the VRML standard thought
> of our world. Do you think they understood it? Do we completely understand
> it?

It does however make much more sense than the STL format.

Georges M. Fadel 
Associate Professor
Mechanical Engineering Department			Tel: (864) 656-5620
Clemson University					Fax: (864) 656-4435
Clemson SC 29634-0921 USA

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