[Radiance-general] BRTF for glazing (was: experiences with the photon map)

[Lars O. Grobe]

> A remark from me: I never use BRTF in RADIANCE now, since all the
> angular information you put into your model is lost for the glow
> material. That means, if you model a specific sky luminance distribution
> and you are using BTDF-func, no angular information of your BTDF-model
> is used! It is treated lambertian ! And this is especially hard, if you
> want to model a system, which is intended to redirect the bright zenith sky.
>  If I model advanced glazings, I use either standard glass and modify it
> by brightfunc or for high reflective materials I use a mixfunc of glass
> (+brightfunc) and metal. I always check the angular transmission and
> reflection of the model by a virtual measuement - and I also test, if it
> still works for the sky.
Hi Jan, hi list,

one more late reply to this. At the moment I am setting up the materials 
for a model with known specifications for the glazing, but I do not have 
samples to measure. So if I want to get a material description e.g. for 
a double-glazing including coating and such, I use the script glaze to 
have some reasonable values that I could not produce else (and I can 
write this down as a reproduceable routine for the docs). I could use 
Optics and access the glazing database, but for some strange reason it 
requires administrator access to a Windows maching that I do not have at 
the moment (did anyone manage to open the database file using something 
like Openoffice?) - but also Optics would give me brtf modifiers.

Did anyone try to model such glazings in radiance, using dielectric and 
interface? What are you using for defining glass panes if no samples to 
measure are available? Ah, and one more question (which leads me back to 
the idea of modeling glazing), what about glazings that consist of 
laminated glass panes + non-uniform laminate (such as printed screens 
for sun protection or advertising), would it be possible to model these 
using dielectric&interface, having one (very) thin layer for the 
laminate modified by a pattern and two dielectric layers of glass on 
both sides? Is it complete nonsense to try modeling such layers 
geometrically (there will be a limit as the thinnest layers surfaces may 
get too close to each other)? Or is all this trouble about considering 
the coatings and such only introducing error, and a simple clear glass 
definition ignoring the coating would still be "better" to use?

TIA&CU... Lars.