[Radiance-general] trans material - tspec comparison

[Shrikar Bhave]

Thanks a lot Andy, Jan et all, you guys make this list amazing!

It was indeed trial and error. Unfortunately, I don't think I can offer a
decent method for setting the roughness yet - Only good news is that it
does change proportionally as expected.
Just out of curiosity, how much of an effort would it be (re time and money
both) for translucent glazing manufacturers to get the testing done from
LBNL?

Thanks again,

Shri


On Thu, Aug 14, 2014 at 9:53 AM, Guglielmetti, Robert <
Robert.Guglielmetti at nrel.gov> wrote:

> T&E's how I've always done it. =/
>
> On 8/13/14, 5:37 PM, "Andrew McNeil" <amcneil at lbl.gov<mailto:
> amcneil at lbl.gov>> wrote:
>
> Ah, good point with the roughness. The only way I know how to get a good
> value for the roughness parameter is trial and error it until it looks
> about right in a rendering - which is probably why I avoid using it. If
> anyone has an good method for setting roughness please share!
>
> Andy
>
>
> On Wed, Aug 13, 2014 at 4:38 AM, Jan Wienold <jan.wienold at epfl.ch<mailto:
> jan.wienold at epfl.ch>> wrote:
> Hi Shri and Andy,
>
> I think you can "spread" the "direct" component when applying a roughness
> to the trans material. Then, the scattered light is not lambertian any
> more. You can control the scattering "width" by the roughness.
> You can see the difference then if you look directly onto the material
> (smaller or larger spot towards sun direction).  Getting different patches
> on the wall etc. is quite hard I guess. The reason for this is , that as
> soon as the "direct part" is scattered (when applying roughness), it is
> handled by the ambient calculation and it is not part of the direct
> calculation any more.
>
> Using a BSDF with a fine resolution is in fact the best way to handle this.
>
> good luck,
>
> Jan
>
>
> On 08/13/2014 01:26 AM, Andrew McNeil wrote:
> 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
> <mailto: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
>
> _______________________________________________
> Radiance-general mailing list
> Radiance-general at radiance-online.org<mailto:
> Radiance-general at radiance-online.org>
> http://www.radiance-online.org/mailman/listinfo/radiance-general
>
>
>
>
>
> _______________________________________________
> Radiance-general mailing list
> Radiance-general at radiance-online.org<mailto:
> Radiance-general at radiance-online.org>
> http://www.radiance-online.org/mailman/listinfo/radiance-general
>
>
> _______________________________________________
> Radiance-general mailing list
> Radiance-general at radiance-online.org<mailto:
> Radiance-general at radiance-online.org>
> http://www.radiance-online.org/mailman/listinfo/radiance-general
>
>
>
> _______________________________________________
> Radiance-general mailing list
> Radiance-general at radiance-online.org
> http://www.radiance-online.org/mailman/listinfo/radiance-general
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.radiance-online.org/pipermail/radiance-general/attachments/20140814/f5431185/attachment-0001.html>