[Radiance-general] trans material - tspec comparison

[Andrew McNeil]

Shri,

In the images you sent I suspect that the sunpatch is over exposed, so it
appears white in all three renderings. If you create a falsecolor rendering
you'll likely see that the sunpatch has different luminance values (make
sure to set the scale sufficently high).

One of the drawbacks of using Radiance's trans material to model
translucent fenestration materials is that the transmission is divided into
strictly specular and diffuse. The specular component is not scattered at
all, and the diffuse component is completely lambertian. You might have
expected the sunpatch to soften and broaden as the diffusion increases, but
with the trans material the shape of the sunpatch doesn't change as
diffusion increases, it just reduces in intensity.

To study diffusion like this, you'll really want to use a BSDF. Probably
also a tensor tree BSDF so you get sufficient accuracy in the sun patch.
And unfortunately LBNL hasn't measured BSDFs for diffusing glazing, so I
can't offer an immediate solution.

Best,
Andy




On Tue, Aug 12, 2014 at 3:51 PM, Shrikar Bhave <shrikarbhave at gmail.com>
wrote:

> Hello All,
>
> For tspec comparison,  I rendered the same scene for four different tspec
> values of 10%, 50%, 90% and 100% (ideal diffuser).
>
> I was expecting varying amount of diffusion, but I am getting puzzling
> results. only 100% (ideal diffuse) value returns no direct sun-patch. All
> the other values show a clear sun-patch in the space.
>
> Any clue why this is happening? Would you expect such results? Everything
> else is constant in the model. (images are attached)
>
> Thanks,
>
> Shri
>
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