[Radiance-general] Glass transmittance

[Ali Fatoorechi]

Thanks for the reply Greg,

Yes I did change the cosine=Rdot.
I have uploaded the radiance oct/rad/script files in this link
<https://drive.google.com/drive/folders/0BwxvtmE7yeVKLVktQ3hWck1YY3c?usp=sharing>.
Not sure you get a chance to look at this but I couldn't understand the
reason for the difference between the results.

Best wishes,


Regards,

Ali Fatoorechi
MBS Survey Software Ltd

*62 High Street*


*SteyningWest SussexBN44 3RD*

*T +44 (0)1903 879323M +44(0)7830751409 <+44%207830%20751409>*
ali at surveymbs.com
www.surveymbs.com

On Tue, Mar 7, 2017 at 4:35 PM, Greg Ward <gregoryjward at gmail.com> wrote:

> Did you remember to change your gtrans.cal file to set "cosine=Rdot"
> instead of your formula, which gives negative cosines?
>
> -Greg
>
> *From: *Ali Fatoorechi <ali at surveymbs.com>
>
> *Date: *March 7, 2017 6:20:43 AM PST
>
>
> Many thanks for the prompt reply Greg,
>
> I appreciate the glass material perhaps describes the glazing more
> accurately.
>
> bf trans Glass1
> 0
> 0
> 7 1 1 1 0 0 1 1
>
> So defining trans material as above means only the specular transmittance
> is left and diffuse part(transmittance/reflectance) is zero[?] This seems
> to be what I am looking for, but I am not sure what I've done wrong
> as the values don't agree(Radiance gives 3.20, CIE report(and our
> software) 3.77). Modifying bf function to return 1 treats the material just
> as an opening(no coefficient applied) which is expected I guess.
>
> Regards,
>
> Ali Fatoorechi
> MBS Survey Software Ltd
>
>
> On Mon, Mar 6, 2017 at 8:45 PM, Greg Ward <gregoryjward at gmail.com> wrote:
>
>> Helo Ali,
>>
>> If you have the formula that accounts for the presence of the window in
>> your opening, you should not apply it to a "glass" surface.  The Radiance
>> "glass" type does an exact calculation of transmission and reflection as a
>> function of incident angle, which your polynomial approximates.  If you
>> want or need to use the formula, then switch out your glass for:
>>
>> void brightfunc bf
>> 2 val gtrans.cal
>> 0
>> 0
>>
>> bf trans Glass1
>> 0
>> 0
>> 7 1 1 1 0 0 1 1
>>
>> Note that you need to use "bf" as the modifier to your trans material to
>> see its effect.  (Your original model used "void" which ignores the
>> brightfunc entirely.)
>>
>> You should also use "cosine=Rdot;" in your cal file, or change the sign
>> of your calculation, which will always produce a negative cosine value in
>> this case.
>>
>> Finally, you should feel free to try using the "glass" type with the
>> correct transmission value, which you can calculate from your formula,
>> which yields 0.87881 as the transmittance at normal incidence, and the
>> trans.cal file, which says transmission should be 0.95712, assuming an
>> index of refraction of 1.52:
>>
>> void glass Glass1
>> 0
>> 0
>> 3 0.95712 0.95712 0.95712
>>
>> I'm hoping the results should be the same between the two descriptions.
>>
>> Cheers,
>> -Greg
>>
>> *From: *Ali Fatoorechi <ali at surveymbs.com>
>>
>> *Date: *March 6, 2017 8:18:00 AM PST
>>
>>
>> Hi Guys,
>>
>> I am fairly new to Radiance and am trying to test one of the CIE
>> Technical Report test 5.10 "Sky Component under a roof glazed opening".
>> There is only one window that is a 1m x 1m opening with 6mm clear glass
>> that serves a 4m x 4m x 3m room.
>> The formula for directional transmittance is defined in the report as the
>> one in this webpage:
>> http://naturalfrequency.com/Tregenza_Sharples/Daylight_Algor
>> ithms/algorithm_2_34.htm
>>
>> The Sky Component value for the opening(assuming no glazing is used)
>> matches the report results but on introducing the glazing, Radiance gives
>> slightly lower results.
>> I am testing this test case against our own software too. Multiplying
>> the above directional transmittance to the radiance value along each ray
>> gives the correct result which is inline with the report.
>> But for some reasons I cannot get same from Radiance. I have set the transmissivity
>> of the glass to 1 but am not sure what value should I use here?
>> In other words if I want to scale the radiance along a ray by the above
>> formula only, how should I define the glazing?
>>
>>
>> The window rectangle is defined as two triangles
>>
>> void brightfunc bf
>> 2 val gtrans.cal
>> 0
>> 0
>> void glass Glass1
>> 0
>> 0
>> 3 1 1 1
>>
>> Glass1 polygon triangle1
>> 0
>> 0
>> 9 (3 coordinates here..)
>> Glass1 polygon triangle2
>> 0
>> 0
>> 9 (3 coordinates here..)
>>
>> The "gtrans.cal" file is defined as below based on the formula given on
>> the above link:
>> cosine =  Dx * Nx + Dy * Ny + Dz * Nz;
>> val = -.028378 + (3.156075 * cosine) - (3.058376 * cosine * cosine) -
>> (1.428919 * cosine * cosine * cosine) + (4.014235 * cosine * cosine *
>> cosine * cosine) - (1.775827 * cosine * cosine * cosine * cosine * cosine);
>>
>> Regards,
>>
>> Ali Fatoorechi
>> MBS Survey Software Ltd
>>
>>
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>>
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