[Radiance-general] rendering meshes with interpolated vertex normals

[bob coyne]

Mark, thanks for verifying that this was the problem.

- Bob

Mark Stock wrote:

> 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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>>
>>
>
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