RE: I beg to differ, or Processing scan data into NURBS surfaces. ..

From: Mr.Le Chi Hieu (
Date: Fri Mar 22 2002 - 20:26:10 EET

Dear Mr. Larry and the list,

Many thanks for your suggestions. The main problem is
that the anatomical structures of the human body are
too complex; it normally leads to "un-optimized"
design data structure, which needs to be reformated
for for CAD/CAM/RP applications; and we, the
designers,still depend a lots on the modeling and
Image Processing tools available.

Although we, the CAD/CAM designers, can solve the
complex modeling problems by this way or the others;
it should open for the non-CAD/CAM specialized people
to do biomodeling conveniently; we always need
geometrical modeling tools that help reducing both the
required design skills and time. For my point of view,
to do that, the only way is to develope the concrete
modeling tools for each specific application and to
work closely with the end-users. My colleges in
KULeuven are working closely with People from
Materialise (MIMICS and Magics RP); hopefully the
discussion may open some ideas to the software
developers in the field of Biomodelling so that more
data formats and tools would be available for the
designers to solve the specific application problems.

With best regards,

Le Chi Hieu

> I tend to approach all problems from the mechanical
> Engineers point of view
> (that's how I was trained) so forgive me if I
> misunderstand the problem you
> are dealing with.
> I understand that the STL file allows you to
> visualize the scan data in an
> easier to understand format, but the scan data that
> the STL was created from
> only had 2D sections in it. The MIMICS software uses
> a routine to connect
> the 2D sections (polyline data) by what I would
> imagine is a relatively
> simple process. My sincere apologies to MIMICS
> software developers if I make
> it sound too simple, but you could:
> 1) Extract a (uniform number) point set from the
> polylines of each section.
> 2) Connect the points in numeric order to the
> equivalent number point in
> each adjacent section.
> 3) Map every 3 of the resulting connections as
> triangles.
> 4) Determine the face vector direction of the
> triangle.
> I'm sure that I am over simplifying the process, but
> you get my meaning.
> The STL was created from the same 2D sections that
> could be used to create
> the NURBS sections. By using the STL vector data to
> determine inside and
> outside of the sections, you could automatically
> process the NURBS and break
> them in the correct place. Once that is
> accomplished, NURBS surfaces can be
> constructed that represent the shape of the inside
> and outside surface of
> the bone structure. You would have editable surfaces
> that can be split and
> mirrored just like the STL file, but would be much
> smoother than the STL.
> (And would be able to be imported into most CAD/CAM
> programs.)
> Talk to the MIMICS people and see what they can do.
> If there is a market for
> this type of data output, I'm sure that they would
> be happy to work with
> you.
> Sincerely,
> Larry Blasch
> Lawrence R. Blasch
> Design Engineer
> CAE Systems Administrator

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

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