3d Textures in Stl models

From: Peter H. Gien (71773.3150@compuserve.com)
Date: Thu Feb 15 1996 - 07:27:05 EET

Michael Reese asked:

>>Also I would very much appreciate it if you or anyone could inform me of any
products that do what you described, namely alter the geometry of cad objects
on their skins in a way that creates those textures in a rapid prototyping
model. <<

We have had a development program in-house for several years now regarding the
problem of textures on RP parts in general. Applying the texture as a
perturbation of the STL facets is the *wrong* way to go since you end up with
many millions of facets. In addition, the mapping of textures is best done onto
a parametric surface in such a way that the texture is not unduly distorted. We
have found that texture maps are most easily mapped onto b-spline surfaces
(NURBS or just plain old vanilla b-spline patches.) The texture is added at the
time of slicing the surface. Take any point on the slice, it corresponds to a
point on the surface, and then look up the texture map value at that point. The
component of this map in the x-y plane is what is added to the slice
coordinates. In this fashion, you can create a respectable orange-peel texture
on a sphere. There are still some issues with Moire effects as the texture
interacts with the slice discretization, but this is minor.

Peter H. Gien
POGO International, Inc.

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