|Message: Re: questions about the parameter sigma alpha and ground-, polishedbackpainted||Not Logged In (login)|
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On Fri, 01 Jul 2011 10:22:50 GMT, Mike wrote:
> Dear Peter, > > thanks for your fast answer. I have made a mistake in my previous Email.
> But I meant the following: If the model is unified, the type > dielectric-dielectric and the finish ground and lobe, spike and > backscatter reflection set to 0 only lambertian reflection should > occure. In this case what is than the difference between the reflection > with sigmaalpha=0 and sgmaalpha=1? What is the physical explanation? Is > the physical explanation the following? - sigmaalpha=0 means that there > are no macro facets but there exsists surface roughness, which generates > lambertian reflection? - change of sigmaalpha from 0 to 1 means that > macro facets are formed with an increasing steepness with an increasing > sigmaalpha from 0 to 1. Is this right?
I am afraid that the unified model allows you to specify combinations of input parameters that don't necessarily have physical meaning or "make sense" to a physicist.
If you were to specify sigmaalpha=0 and require every reflection to be lambertian you'll get refracted rays as if the surface is perfectly polished but reflected rays with a lambertian distribution. If, on the other hand, you specify some sigmaalpha>0 you'll also get refracted rays as if there are micro facets but lambertian reflected rays - independent of micro-facets. Moreover, however, the probability of reflection is now based not on the nominal normals but the facet normals. The unified model's four possible reflection probabilities come into play only once Snell's Law has already decided on a reflection.