From: Mike Pratt - MIDT (
Date: Mon Jan 29 1996 - 17:07:20 EET

Peter Gein wrote:

>>Sadly Steve, most solid modelors do not offer this capability,
especialy the inexpensive ones. One point worth making here is that if
you use some nice features such as bosses, tapered holes, and ribs for
example, then when you blast this out to another CAD system via IGES,
you lose the associativity between these elements. For example, try to
move the boss over 2" on the IGES file. You will end up having to move
each surface. Try converting the IGES surface into a solid, and then
remove a counter-bored hole and surrounding boss. You will have to
make quite a number of edits to do this, whereas in the original
system, you can simply remove these elemens from the state tree and
recompute the solid. A state tree is simply a recording of each
feature used to construct the model together with their relationship
to other features.<<

Steve Farentinos wrote:

>Isn't STEP supposed to solve some of these problems? Anybody know
what the status of STEP is? Who has implemented it?<

Most of the major CAD vendors have STEP translators either already
available or under test. The standard (ISO 10303) specifies various
Application Protocols, which provide means for data exchange in
different application areas. The only one of relevance in RP at the
moment is AP203, providing for the transfer of wireframe, surface and
boundary representation solid models. Unfortunately this STEP format
only handles geometry/topology data at present; there is no provision
in the current version for the transfer of parametrized models, or of
models built using constraints and features. This is recognized as an
important limitation, and efforts are currently under way to add the
relevant capabilities to AP203 (I am involved in those efforts).

Another AP under development, not yet part of the standard, is AP214.
This is intended to handle information needed in automotive
applications. It does provide for the transfer of feature data, but
in a limited way. Although this is not yet part of the standard many
vendors (especially those whose systems are widely used by the
automotive industry) have developed experimental AP214 translators.

Incidentally, I have heard rumors of an RP Interest Group starting up
within the ISO STEP community (ISO TC184/SC4), but don't currently
know who is involved.

Mike Pratt

| Dr Michael J. Pratt, |
| National Institute of Standards and Technology, |
| Manufacturing Systems Integration Division, |
| Building 220, Room A127, Tel. (301) 975-3951 |
| Gaithersburg, MD 20899-0001, Fax (301) 258-9749 |
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