[Radiance-general] rendering meshes with interpolated vertex normals

[Mark Stock]

Bob,

Your guess is right. Radiance's triangles, even with normal
interpolation, are still flat. To use the normals to present a 
true curved surface would (I think) require an implicit 
representation of the surface.

This particular example, with a low-res mesh and direct sunlight, 
is the "poster-child" of this problem.

I usually avoid this problem by a combination of higher 
resolution (I use tri meshes up to 1M elements) and more ambient 
than direct light.

So, I see no way to completely avoid this for some problems.

Mark
mstock at umich.edu

On Tue, 13 Dec 2005, bob coyne wrote:

> Hi,
>
> I'm having a problem rendering polygon mesh objects with interpolated
> vertex normals (converted via obj2mesh). I'm running Radiance 3.7.2b
> patch release 22 Aug 2005.
>
> When I render a sphere mesh that's illuminated from above and to the
> side, I get bad artifacts along the shadow line, with large dark
> triangular wedges periodically protruding into the illuminated
> area. (See link below for what this looks like.)  The dark triangles
> seem to correspond to those quadrilaterals in the mesh where only a
> single vertex is illuminated. My guess is that it's treating the whole
> quad as pointing away from the light source, even though one vertex
> and a significant area of it are in the illuminated region of the
> object.
>
> Is there any way to avoid this?
>
> www.semanticlight.com/images/sphere-problem.jpg
>
> Thanks for any help.
>
> - Bob
>
>
>
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