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

[jhkim94 at aesl.hanyang.ac.kr]

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.