Robert Russ (russ++at++sherman.sdsc.edu)
Thu, 9 Jun 1994 17:20:23 -0700 (PDT)
my $0.02 on the nurbs thingy:
The current loaders (ie: for .sgo, .obj, .dxf, etc) are all for handling
polygonal data exclusively for a seemingly very good reason: Performer
eventually needs polygons to render and reading in polygons is fairly
straight-forward - the readers are fairly "dumb" in that they don't
interpret data, only read it in and translate it to the data structure
Performer needs.
On the other hand, a nurbs -> poly's reader requires some smarts to
translate the surfaces into polygons. Important issues pertaining to
subdivision levels, error factors for resolving the surfaces to polygons,
limitations of the target machine, etc are all important in determining
exactly how to represent a spline model with polygons.
We've found it to be much more beneficial to go into a program and
somewhat manually convert spline models to polygons based on the above
concerns. We use Alias for all of our VR stuff and have written a .tri
reader (.tri is a triangle file format Alias creates) which works quite
nicely. Although this isn't as automated as a "spline file reader", it
seems to me that this would be a rather complex issue to automate well.
Rob
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Robert H. Russ russ++at++sdsc.edu
3D Computer Animation / Post Production OFC: (619) 534-5030
Visualization Technology Group LAB: (619) 534-5162
San Diego Supercomputer Center FAX: (619) 534-5152
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On Thu, 9 Jun 1994, Brian Hill wrote:
> Robert Rossow wrote in a previous message related to NURBS
> >
> > I believe that the ability to use NURBS to define geometry within
> > Performer would be extremely beneficial......
> > ...
> > ...
> > If this were the case, many more models would become available,
> > and the user could be relieved of both the tesselation and
> > texture/normal specifications on a per-vertex basis.
> > ...
> > Sounds too good to be true. What do you think?
> >
> As a related matter, almost all of my geometry originates as an
> engineering CAD model (ie NURBS) that has to be converted with a
> combination of automatic and manual techniques. There are times
> when I don't need to develop a pituresque model using exotic
> texturing and materials, I only need a functional rendering.
> It would be nice to be able to load the original IGES NURB data
> into Performer. How about an IGES loader for Performer?????
>
> Thanks,
>
> ===================================================================
> Brian Hill | Advanced Marine Enterprises, Inc.|
> CSD Section Chief | Suite 1300 |
> (703)415-3080 | 1725 Jefferson Davis Hwy. |
> hill_b++at++ameig1.navsea.navy.mil | Arlington VA, 22202 |
> ===================================================================
>
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