Re: VRML, STL and other animals

From: Joe DeGuglielmo (jfdegug@Kodak.COM)
Date: Thu Jan 11 1996 - 13:40:42 EET

>At 06:19 PM 1/10/96 -0500, you wrote:
>>Tony writes:
>>> The surface normal at a vertex can be used to approximate a curved
>>> surface using a planar facet. This is used for Phong and Gourad shading
>>> to create a smooth-looking shaded model using a model with a relatively
>>> small number of facets. For example, if you are defining a sphere, you
>>> obviously can only approximate the surface with facets. What you would
>>> really like to do for shading such a sphere is instead of using the same
>>> color for an entire facet which will produce a visibly faceted surface,
>>> is to gradually change the color of a facet over its surface so that the
>>> color at the edges of the facet match the color of its neighbors, thereby
>>> producing a smooth-looking surface. The way this is done is to use a
>>> normal at each corner that represents the direction that the corner
>>> should actually be facing. This is difficult to explain, but there are
>>> some pictures and descriptions at the following web page:
>>I understand what you're saying, but why do you want to be able to do this
>>with an SLA file?
>>> There are probably others, but this is the first one that I found. This
>>> same smoothing process that is used for shading could be used to smooth
>>> RP parts if that information is included in the file.
>>This would be worthwhile, I suppose. Has anyone explored this idea?
>>Actually it seems promising.
>>Mike New
>What I don't understand here is that this seems to be used to make your
part look smooth on your screen, but what will each layer cross section look
like? Are we not still working with the same facet that has been colored
>Joe D


Joe DeGuglielmo
Eastman Kodak Company
901 Elmgrove Road
Rochester, NY 14653-5315

Rapid Prototyping Center Established 1988
Selective Laser Sintering

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