BRTF for glazing (was: experiences with the photon map)

radiance-general
1

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.

2

Hi,

For glazing definition we always use BRTDfunc material, which we define
partly automatically partly manually.
We export each glazing layer from Optics5 (I don't have idea what you can do
whan you don't have access as administrator), and then combine them in BRTD
func. If no data in Optics5 database, we use some estimated values for
transmittance and reflectance.

For transmittance/reflectance functions of each layer we use functions used
in glaze output. For coated glazing also. I think glaze.csh has some
functions for laminated glass too, but not sure.

Marija.

Hi Jan, hi list,

ยทยทยท

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.