[Radiance-general] Question regarding the BRTDFunc...

[Greg Ward]

Hello Ji-hyun,

I was very embarrassed to find the following message sitting in my  
"InBox," apparently unanswered.  Did anyone else write to you about  
this?  It must have come at a busy moment and was forgotten in my  
pile, so I apologize.  Let me know if you are still struggling with  
this, and I'll compose a proper response.

Basically, you should have a look at the "glaze" script included with  
Radiance.  Jack de Valpine of Visarc requested and sponsored its  
development, and the script is specifically targeted at multi-pane  
window systems.  It generates a BRTDfunc, which you may use as a  
guide in your process.

Again, I am very sorry for the delayed response.

-Greg

> From: jhkim94 at aesl.hanyang.ac.kr
> Date: October 22, 2007 8:08:49 AM PDT
>
> Dear Dr. Ward.
> Hello. My name is Ji-hyun Kim, majoring Architectural Visual  
> Environment at
> the Hanyang graduate school in Korea.
> I hope this e-mail will not bother your busy time.
>
> Now, I am analyzing solar specular reflection effect by buildings'  
> coated
> glass with the RADIANCE program.
> The purpose is to measure characteristics of coated glass materials  
> which
> are considered in real design process and to make a simulation  
> applying the
> data.
>
> In order to figure out the characteristics of ordinary materials, I  
> used
> Spectraphotometer to measure reflectance value and input the other  
> data,
> I could not see solar specular reflection effect clearly so I have  
> tried to
> use BRTDfunc option to make a simulation of coated glass  
> materials'BRDF
> characteristics.
>
> While I was looking for the research materials, I found out that  
> the input
> data of BRTDFunc option is various as below.
>
> Mod BRTDfunc id
> 10+ rrefl  grefl  brefl
>      rtrns  gtrns  btrns
>      rbrtd  gbrtd  bbrtd
>      funcfile   transform
> 0
> 9+  rfdif  gfdif  bfdif
>      rbdif  gbdif  bbdif
>      rtdif  gtdif  btdif
>      A10.
>
> I roughly understood the definition of input data. I tried to find  
> out what
> method I can use to measure it but I could not find the suitable
> information.
> So I would like to ask you some questions.
>
> 1. When I simulate materials, which I use in real, on RADIANCE, how  
> I can
> measure the input data that is needed in RADIANCE,
> and how I can divert the measured data to BRTDfunc input data such  
> as rrefl,
> rfdif, rbdif. rtdif etc. in order to apply it?
>
> 2. Ordinarily BRDF is defined by intensity of the wavelength  
> according to
> altitude angle of incident light and azimuth angle and altitude  
> angle of
> reflected light and azimuth angle.
> I figured out that the dat file by four values above is needed like  
> IES file
> but I could not find the data about applied cases and composition  
> of dat
> file.
> Is there any method to use data in dat file form? If there is, I  
> wonder how
> I can make dat file form.
>
> If it is possible, I am going to use gonioreflectometer, which we  
> made, to
> measure and apply BRDF data in artificial sky-dome.
>
> 3. In case of LBNL_glz\blue_refl.rad file in DATABASE of Desktop  
> RADIANCE,
> BRTDfunc is defined as below.
>
> void 	glass 	blue_refl_glass	
> 0
> 0
> 3	0.206104	0.194473	0.17589
>
>
> void 	BRTDfunc	blue_refl_front	
> 10	
> 	0.188941	0.178277	0.161239	
> 	0.356133	0.400754	0.340173	
> 	0 0 0
> 	.	
> 0
> 9 0 0 0 0 0 0 0 0 0	
>
> void 	BRTDfunc	blue_refl_back	
> 10	
> 	0.188941	0.178277	0.161239	
> 	0.084167	0.17056	0.175861	
> 	0 0 0
> 	.	
> 0
> 9 0 0 0 0 0 0 0 0 0	
>
> I think this case is a bit different. The part of void  BRTDfunc
> blue_refl_front, I think blue_refl_glass is suitable instead of void.
> I understood that when identifire is void it is defined as a new  
> material so
> I wonder what kind of definition is made above.
> Also, when it set up blue_refl glass material, all input data  
> related to
> diffuse reflection have 0 values. It means that diffuse is not at all
> considered?
> In my opinion, when I simulate BRDF effect by coated glass the values
> related to diffuse reflection would be important. How about your  
> opinion?
>
> 4. While I was studying related materials, I found rayinit.cal file,
> glazing.cal file and glaze1.cal file.
> In case of Glazing.cal file, reflectance and transmittance of  
> coated glazing
> are measured by using window 4 programs.
> In my opinion, the RADIANCE option we needed is using glazing.cal  
> file and
> it depends on clear and bronze-coated glazing.
> When I apply the glazing.cal file on various coated glasses, how  
> can I set
> up the variables to simulate?
>
> Could you give me advice about the way of simulation or setting  
> rendering
> option of rpict command
> when I simulate glare due to the solar specular reflection?
>
>
> I am using RADIANCE program personally. I fully understand how to  
> make basic
> image but
> I have a trouble with understanding of making and revising cal file  
> and
> Function File so it is difficult to use RADIANCE Program entirely.
>
> I am waiting your advice to make the best use of RADIANCE.
>
> Sincerely your,
> Ji-hyun Kim.