"Solidifying" STL - How to get the shell only?

From: Robert Roy (robroy@pobox.com)
Date: Thu Jun 05 1997 - 02:04:01 EEST

Hi all,

(I have already sent this message once before (to rp-ml@ltk.hut.fi) but
haven't seen it show up in the list, so here goes again)

We are attempting to slice an STL file of an object produced using a
visual-rendering-oriented modelling system (a figurine from Lightwave in
this example, but it's the general solution I'm after).

The output form this class of software is normally intended only for
visual rendering and is not "solid-oriented". Features added to the
surface of the figurine extend through the surface into the interior,
and the internal "walls" of the blocks used to define the features
survive in the interior. Put another way, when constructing the model
the boolean union of any two "solid" or enclosed areas has resulted in
the combination of both meshes, NOT the "outsides" only of the two

To make life even more difficult, there are of course overlaps in the
surfaces and large gaps between edges. This does not present a problem
when rendering for TV or print but makes RP prep a nightmare.

We have Magics RP here that seems to do a good job of repairing small
gaps and minor errors but it's far too time consuming for major repair
work. We need a simple method of removing everything except the outer
shell, perhaps with adjustable tolerance for gap width.

Any ideas? We have played a little with the trial version of DeskProto,
an STL to NC machining package, but that doesn't seem to have a way of
outputing anything other than tool paths - no good for our Sanders
ModelMaker! We ultimately need a repaired STL output, although we could
go via Wavefront (.OBJ), DXF (rather not!) or even SolidWorks (.PRT,
.SAT etc).

Thanks for your help.


| Rob Roy    robroy@pobox.com    | Protoforté Pty Ltd - RP Bureau     |
|  Castle Hill, NSW, Australia   | Sanders ModelMaker VAR for Aus/NZ  |
|P+61-2-98942995 F+61-2-98942868 |   Go to www.pobox.com/~protoforte  |
|       Protoforté - "The Precision Edge in Rapid Prototyping"        |

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