We should take a step back and look at Rev Eng and the reason for using
NURBs to model the data. If you are going to scan an object and turn around
and create an STL file then there is no need to go to a NURBs model first.
NURBs or any other mathematical model is an approximate representation of
your model. The reason for going to a mathematical model is that it is
easiar to edit and modify and results in "data reduction" as an aside. After
all how can the NURBs approximation be better than the original scan data,
assuming for the moment that the scan data is true "reflection" of the
object.
A good NURBs modeler should recreate a straight line or planar face truly or
the modeler or the algorithm is not right.
I dont quite agree with some of the things that joe sims says here or
possibly am misunderstanding them here. In particular ..
"Reverse Engineering requires more correction than accuracy..if you are to
use spline to define the accuracy of your digitised workpiece than it will
not give you the surface
quality that you wants....because every segment of straight lines does not
constitute to a well-defined curve. "
is rather ambiguous and not correct ...
Dont wish to start a flame war but I just disagree with it.
---------------------------------
Dr. Anshuman Razdan
Technical Director PRISM
Email: razdan@asu.edu
Web: surdas.eas.asu.edu/~razdan
MC 5106 Arizona State University
Tempe AZ 85287-5106
Phone: (602) 965 5368
Fax: (602) 965 2910
> -----Original Message-----
> From: owner-rp-ml@ltk.hut.fi
> [mailto:owner-rp-ml@ltk.hut.fi]On Behalf Of
> Innomation Systems & Technologies Pte. Ltd.,
> Sent: Monday, January 25, 1999 5:14 AM
> To: rpmail
> Subject: Fw: Newbie's opening volley.
>
>
> Dear Paul,
>
> pardon me if i am wrong if you have only spline
> surfaces...then most of
> your jewels look like straight cuts will it???
>
> for reverse engineering, i still think that NURBS will still
> be the best
> ....if not...then most of your efforts to integrate Reverse
> Engineering
> into your design will be lesser significant.
>
> personally, i feel that Reverse Engineering requires more
> correction than
> the accuracy.....if you are to use spline to define the
> accuracy of your
> digitised workpiece than it will not give you the surface
> quality that you
> wants....because every segment of straight lines does not
> constitute to a
> well-defined curve.
>
> i am not sure about the notations used in the IGES file(text
> based)....but
> i do remember that for NURBS surface you are more likely to
> see non-uniform
> length describing the surface equation parameters...while for
> splines or
> lines you can notice a more uniform pattern.
>
> well, don't try to understand the IGES text file...you can
> get crazy by
> doing so....i will suggest that you use software like
> Surfacer or Rhino3D
> to view the IGES surfaces.
>
> Sincerely,
> joseph sim
>
>
>
> ----------
> > From: Paul Burr <tigerpb@ids.net>
> > To: rapid proto. list <rp-ml@bart.lpt.fi>
> > Subject: Newbie's opening volley.
> > Date: Monday, January 25, 1999 10:21 AM
> >
> > Greetings fellow listers! As a first timer to this list I'm looking
> > forward to the insights of this group.
> > I'm currrently designing costume jewelry using JewelCad
> (any other users
> > out there?) and building the parts on a Sanders MM2. I've
> also have used
> > the Sanders MM6 Pro previously.
> > Anyway my employer, Giovanni Jewelry (100 Nashua St,
> Providence, RI ) is
> > looking to expand our capabilities with 3D scanning. This
> is a new area
> > for us, and we'll need all the advice I can gather.
> > I'd like to retain JewelCad as our design front end, at
> least for the
> time
> > being. It is capable if importing only igs files that are
> spline surface
> > iges.
> > So, my question is two fold: How does one tell the
> difference between
> > spline and non spline iges files?
> > and, are there any file translation packages that can tweek scanner
> output
> > into the "flavor" that I need?
> >
> >
> >
> >
> > For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
>
> For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
>
For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
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