Re: More on STEP

From: Delft Spline Systems (
Date: Mon Feb 16 1998 - 12:04:47 EET

Terry Wohlers wrote

>... There have been discussions over the
>years, even in recent months, to develop a replacement or alternative to
>STL. Getting CAD developers to support yet another output format would
>take more blood and sweat than most of us care to shed. Why not 1) carry
>"STL data" within the STEP file (as Mike said, STEP AP203 already contains
>a faceted boundary representation), 2) ask the RP system manufacturers to
>support STEP, and 3) let the user decide whether to use STL data or precise
>math surface data (which STEP also carries) when building an RP model?
>What could be easier and more flexible?

Hi Terry,

The idea of integrating STL and STEP into one format that would cover
all types of geometry exchange does indeed appeal.

However, I see disadvantages too.
The main issue is that STEP is a complicated format, due to the need to
cover all types of CAD-data (also non-geometrical). This will lead to a
necessity to have a discussion between sender and receiver before the
data exchange: 'Can you export in STEP part 42 format or do you only have
41 ?' ' Does your STEP translator support AP 203 ?' etc.
Just the type of discussion we absolutely do not want.

The BIG advantage of STL is that it always works ! No discussion needed.
So my idea would be to use STEP only in case needed, that is only in
case the geometry needs further modelling and all non-geometric information
(like topology, parametrics etc) must be transferred as well.
For ptototyping let us stick to STL.

Compare it with word-processing:
you can choose here to transfer using a proprietary format (STEP not yet
invented here) including all special data, or to transfer using Postscript
(having the role of STL). The big advantage of the latter is that you can
allways print it on a PS printer , regardless of the type of wordprocessor
you are using. It is not the most efficient format, but it does work.


Lex Lennings.

Delft Spline Systems, The Netherlands.
We offer DeskProto: affordable Rapid Prototyping using CNC milling

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