[Radiance-general] Import from Optics5

[Jack de Valpine]

Hi Marija,

Although Optics5 is a great resource for glazing information. The 
radiance materials that get exported are perhaps too simplistic 
depending on how they are to be used. The three definitions that are 
output are 3 options to be chosen from, you do not use them all at the 
same time.

The glass definition (GlzSys_glass) really only represents the correct 
transmittance for the exported glazing system, the front and backside 
reflectance are equal and relatively low, ~7% (I do not remember for 
sure, so Greg will have to provide the authoritative answer on this one).

The two BRTDfunc definitions are really only useful for the selected 
condition (eg if you are inside or if you are outside). These two 
materials are dependent on the geometry being built with the surface 
normal pointing the correct way and uniformly for that class of 
geometry. A simpler way  to combine these two materials into one 
definition is as follows:

void BRTDfunc GlzSys_front_and_back
10
    if(Rdot, 0.134, 0.134) if(Rdot, 0.147, 0.147) if(Rdot, 0.147, 0.147)
    0.740 0.803 0.779
    0   0   0
    .
0
9 0 0 0 0 0 0 0 0 0

In the case of your exported example, it looks like the front and 
backside reflectances are the same. Here is how to interpret this 
definition:

void BRTDfunc GlzSys_front_and_back
10
    if(Rdot, <r_front_refl>, <r_back_ref>l) if(Rdot, <g_front_refl>, 
<g_back_refl>) if(Rdot, <b_front_refl>, <b_back_refl>)
    <r_trans> <g_trans> <b_trans>
    0   0   0
    .
0
9 0 0 0 0 0 0 0 0 0

The "if" statement determines if the ray hits the front or back of the 
geometry, if it is positive then it takes the first value, if negative 
it takes the second value. You need to determine what front/back means 
though (eg front==exterior and back==interior).

NOTE that these BRTDfunc definitions do NOT account for angular 
dependencies of transmittance/reflectance of the material.

Another options is to take the transmittances and reflectances for the 
various surfaces (eg s1 through s4) and use them with the "glaze" script 
found in radiance. This creates a more sophisticated material 
representation for single and double pane type of glazing systems. To do 
this though you need to export radiance files from Optic5 not for the 
final assembly of the glazing system but for the individual sub layers.

Regards,

-Jack de Valpine

Marija Cvetkovic wrote:

> Hi,
> I am trying to use actual data for glazing materials, and I've found that
> Optics5 has a good database. Since it has exporter to Radiance, single or
> multi layer glazings can be easily converted to Radiance format.
> Resulting file has a form like:
>
> void  glass       GlzSys_glass
> 0
> 0
> 3     0.807     0.875     0.849
>
> void  BRTDfunc    GlzSys_front
> 10
>      0.134     0.147     0.147
>      0.740     0.803     0.779
>      0 0 0
>      .
> 0
> 9 0 0 0 0 0 0 0 0 0
>
> void  BRTDfunc    GlzSys_back
> 10
>      0.134     0.147     0.147
>      0.740     0.803     0.779
>      0 0 0
>      .
> 0
> 9 0 0 0 0 0 0 0 0 0
>
> My question is how should I use these data in Radiance scene description.
> I suppose that idea is to define window glass with 3 layers:
> GlzSys_front  GlzSys_glass  GlzSys_back
>
> Am I right?
>
> One more question: does anyone know how this BRTD parameters are 
> calculated from Optic5 data?
>
> Thanks,
> marija
>
>
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>

-- 
# Jack de Valpine
# president
#
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