RE: I beg to differ Re: Stupid STL Question

From: Blasch, Larry (
Date: Wed Mar 20 2002 - 21:41:05 EET

Dear Mr.Le Chi Hieu,

What are you creating the STL file with... that you want to edit with cheap

Most biomedical models are created from extremely expensive scanning
equipment (MRI, X-ray, CAT, 3d laser...) and then processed through
specialized software to create the STL data.
Could the input data be processed into something other than STL. Are you
working with a intermediate data format (STL) that is just introducing
greater complexity?

It seems that the data format that you need for the final process (RP) may
not the most appropriate for manipulation or editing. I would look at your
entire process and determine the best format for each step. Many CAD
packages do a great job of exporting STL data. I don't know of a single one
that does a good job of editing an STL file.

Larry Blasch

Lawrence R. Blasch
Design Engineer
CAE Systems Administrator
OPW Fueling Components
P.O. Box 405003
Cincinnati, OH 45240-5003 USA
Voice: (513) 870-3356
Fax: (513) 870-3338

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-----Original Message-----
From: Mr.Le Chi Hieu []
Sent: Wednesday, March 20, 2002 11:17 AM
Subject: RE: I beg to differ Re: Stupid STL Question


> STL input into Pro/E is optional with one of the
> advanced surfacing packagesthat cost more money.

Pro/ENgineer and UG (from version 18, UG17 or less can
only view the STL files)provide some "editing" tools
for STL files. Besides the expesive cost spent for the
packages, the modelling process, however, requires
lots of design skills (this must be taken into
account, especially when the non-CAD/CAM people such
as surgeons who would like to do Biomodeling as
discused recently on the list) and times for the
modeling of complex free-formed surfaces (the ones in

Because, to "edit" the STL files (not only Hollow,
Boolean, Off-set, Cut etc.), we must convert the
triangle mesh into the the parametric based
representation (NURB or Free-Form sculpting, etc.);
this can be done in the Reverse Engineering Software
like Surfacer from Imageware. The Surfacer is also
expensive too. In addition, if we would like to get a
"nice" surface, we need to reconstruct the basic CAD
entities (point, splines contours, etc.)from which the
surface is modelled.

Moreover,to edit the STL files by converting the
triangle surface into the parametric based surfaces,
normally we have to do that in the interactive way
(manually editing). It takes lots of time and
sometimes it is quite dificult to get the smooth
free-form surface (or we have to expense the accuracy
loss in the modelling). It sometimes also makes
difficult for CAD/CAM manipulation during the design
process because of the high degree of the mathematical
description of the surfaces (a large amount number of
control points used).

I am waiting for some cheap tools to convert the STL
surface into the "editable" surfaces, which are stable
and familiar with the CAD/CAM designer: NURB based
modelling (both surface and solid).

With best regards,


Mr.Le Chi Hieu
The Biomodeling Group, ISE.SAT.AIT
Bangkok, Thailand

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