[Radiance-general] Specular convex reflector and surface normals?

[Gregory J. Ward]

Hi Lars,

If you use the "mirror" material type for the ceiling, it will cast  
appropriate source reflections, but without the surface normal  
interpolation.  Also, it will incur a lot of calculation overhead,  
proportional to the number of triangles in your ceiling.  I don't  
think I'd recommend it for that reason.

Surface normals are interpolated for other parts of the calculation,  
such as the diffuse indirect, which in your case is not so diffuse.   
This is no doubt the source of your splotches, and the photon map  
addition may well take care of the problem.  You could try it with  
the "mirror" type first, just to see how long it takes and what it  
looks like.

-Greg

> From: "Lars O. Grobe" <grobe at gmx.net>
> Date: May 14, 2007 1:10:30 AM PDT
>
> Hi,
>
> one question regarding "rounded" surface normals on specular  
> surfaces. I have a dome with a highly specular (consider 99%  
> specular) surface. The dome is an obj-mesh, with interpolated  
> vertex normals ("smooth") and imported using obj2mesh.
>
> The rounded vertexes render a smooth dome when viewed from below,  
> as expected. But as this dome reflects light onto the floor, it is  
> some kind of a big convex reflector. I wonder if for light  
> reflected from this reflector to the ground, the normal  
> interpolation is applied, too. The background for my question are  
> big bright splotches on the floor. I also wonder if this geometry  
> is something not really to be modeled in classic radiance, as the  
> old questions of convex reflectors and backward raytracing might  
> occur. Is this even a case for photon mapping? I have never been in  
> modeling a convex reflector, for architecture this is not a typical  
> example in our days, so I am curious about what you propose...
>
> CU Lars.