[Radiance-general] Redirecting+scattering

[Jan Wienold]

Hi  Federico,

your task cries for using photon-mapping...

You should model your shading system geometrically and use dielectric as 
material (be careful about the surface orientation!). The diffusing 
material can be modeled by trans material. If you have a complex 
scattering material, you can adapt the trans material by an cal 
function. (Don't use BRTF-func or data with the current photon-mapping 
version).

To be more efficient using the diffuse sky, you should define a 
photon-port, where all the photons are emitted to. Usually the 
photon-port material is the window pane.

Then you can simply run the simulations, direct and diffuse 
contributions should be calculated correctly.

Last but not least, there exist also a version of daysim containing 
photon-mapping, so you can run these simulations also hourly (or other 
timesteps) if you want. Unfortunately, the latest daysim version didn't 
compile with the photon-mapping extension - but if you need it, you can 
use also the older version, Christoph could provide it.

Good luck!

Jan

Federico Giovannetti wrote:

> Hallo Greg Ward, hallo Radiance Community!
>  
> I've been learning Radiance for a couple of weeks and i have to work 
> intensively with it in the next weeks, as I´m investigating the energy 
> saving potential and visual comfort of systems combining angular 
> selective and diffusing panes.
>  
> Now I have to simulate a simple test-room with a complex fenestration, 
> which includes an exterior prismatic structure as shading device and a 
> diffusing pane for glare control. I try to find out the best way to 
> model the system so as to get quantitative accurate results (RwR 
> Chapters 10-13 and mails archive) but i´m still a little bit confused....
>  
> - As to the prismatic structure, i will use the PRISM2 material as 
> virtual source. No redirection of diffuse incoming light and no 
> dispersion are the only limitations of this material. And it would 
> make no sense to use the PhotoMap port, because these materials are 
> not implemented in this tool.  Is it right?
>  
> - As to the diffuser, i would intuitively treat it as an ILLUM with a 
> BRTDF function as alternate material (I´m measuring, modelling and 
> comparing different kind of diffusers) and run  MKILLUM.  If 
> i understood correctly, the BRTDF materials are only considered in the 
> direct calculation and indirect specular, but not in the indirect 
> diffuse, where they are approssimate to lambertian diffusers. Should i 
> try another material?
>  
> - How are PRISM materials computed in the MKILLUM calculation of the 
> window light output? Should I better try to run the simulation without 
> MKILLUM and high ambient parameters (-ab, -ad, -as)?
>  
> - What if i measure the BRTDF of the complete system and i model it as 
> a normal light source? It is really difficult (or impossible) to get 
> sharp peaks in light output with  high subsampling and jittering of 
> the source? 
>  
> Any other suggestion to simulate this system correctly (quantitative)? 
>  
> Sorry for so many questions and THANKS A LOT for any contribution.
>  
> Regards,
> Federico Giovannetti
>  
> ---------------------------------------------------------
> Federico Giovannetti
> Institut für Solarenergieforschung GmbH
> Am Ohrberg 1
> D-31860 Emmerthal
>  
> tel:        +49(0)5151-999-501
> fax:       +49(0)5151-999-500
> e-mail:   f.giovannetti at isfh.de <mailto:f.giovannetti at isfh.de>
> internet: www.isfh.de <http://www.isfh.de>
>
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