Re: VRML instead of STL

From: Marcus Joppe (
Date: Thu Jan 04 1996 - 17:37:50 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.
> 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 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?

If you see this topic only from a mathematical or physical view on
producing parts with a RP-Machine I agree with you. The use of VRML
doesn't bring an direct mathematical or physical improvement to RP,
nor is it useful to work with polygons in an RP-Machine.
But if you see this topic in bigger terms of Rapid Product
Development, you can't limit your view only on the RP-Machine. In my
opinion you can see the RP technology as a CAD/CAM process
chain divided in three main subjects:

Geometric Modelling --> RP Process Planning --> RP Part Building

Geometric Modelling:
The goal of this subject is the mathematical representation of a
physical object in a digital equipment. It is not only limited to
CAD. You can also obtain a geometric model from a Laser Scanner, CT

RP Process Planning:
The goal of this subject is the RP process specific treatment of the
part geometry. This means visulisation, verification, part
orientation, support generation etc. and at the end of this subject
slicing of the part. If you not only limit this topic to geometrical
aspect, you can add organisational aspects like build time or cost
estimation, material or process selection etc.

RP Part Building:
The goal of this subject is the building of the part on a RP machine.
This includes also selection of build parameters, surface
treatment or other post-processing steps.

Because the different subjects of the process chain are often done
by different people of different departments and/or companys you
need data exchange formats for the connection between them. This
means there is a need of visualisation, communication and sharing
information between different places. By using a standard like VRML,
which isn't restricted to RP, you don't have to develop your own
tools for the improvement of this problem. You can use standard
software tools mostly independent from a specific hardware platform
and mostly available as shareware. Beside that we can benefit from a
much more bigger man power in this area. We are not longer sitting in a
rowing boat on a small river, we are then sitting in a big ship on
the ocean. Let's see where we are landing :-)

I don't want to discus which data representation is the best for RP in general. In
the moment I think there isn't a solution for all problems of data
exchange. It depends on the position in the chain and your specific
requirements. But VRML can help to improve the communication and
information task in the process chain.

Ciao ...

 Marcus Joppe
 BIBA - Bremen Institute for Industrial Technology
        and Applied Work Science
 University of Bremen
 Hochschulring 20, D-28359 Bremen, Germany
 PO. Box 33 05 60, D-28335 Bremen, Germany
 Fax: +49/421/218-5510
 Tel.: +49/421/218-5595 or -5542

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