Re: Why are .iv files so smooth?

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Michael Jones (mtj++at++babar)
Sat, 30 Mar 1996 18:33:13 -0800

Nuno writes:
> > When I load teapot.dxf into perfly I can see each polygon.
> >
> > Using DxftoIv to convert it to Inventor format I find that when loading
> > the new teapot.iv into perfly I get a completely different result: The
> > surface is smoothed instead of faceted.
> >
> > Why is this?

This is because the "DxfToIV" program has decided to do you a favor. It thinks
that the faceted geometry in the DXF-format files probably represents a smooth
surface and is doing the following:

 1: computing face normals from vertex positions
 2: using adjacency calculations to identify all
    the faces incident at a vertex
 3: averaging the vertex normals incident at each vertex to compute a
    "smooth" surface normal.

It actually has little to do with OpenInventor or IRIS Performer, it's simply
the case that one converter (DxfToIV) is doing a favor for you (presuming that
you want it smooth, that is) and the other (pfdLoad_dxf) simply loads what's
in the file.

Michael Jones

Be seeing you, Phone:415.933.1455 Fax:415.965.2658 M/S:8U-590
Michael T. Jones Silicon Graphics, Advanced Systems Division
mtj++at++sgi.com 2011 N. Shoreline Blvd., Mtn. View, CA 94039-7311
                    "Du musst Amboss oder Hammer sein" -- Goethe

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