[Radiance-general] DF calculated in Radiance and Relux

[Thomas Bleicher]

On 29 Mar 2008, at 07:21, Per Haugaard wrote:

> Dear Radiance Users,
>
> In order to double check the DF which I calculated in Radiance I  
> also calculated these for the exact same room with all the same  
> settings (reflectance, transmittance, dimensions, areas of the  
> pane, reference plance, reductions factor = 1 in Relux and city  
> (Oslo)) in Relux .
>
> Surprisingly since Relux is based on Radiance the DF which I  
> calculated in Radiance are about 1.7 higher than the ones  
> calculated in Relux (DF calculated in Radiance = 17 and the ones  
> calculated in Relux = 15,3 0.6m from the facade).

Are you sure Relux is based on Radiance? According to my knowledge  
only the visualisation
add-on 'Relux Vision' is Radiance based. The calculation part uses  
another approach (radiosity
I think).

Anyway a difference of 70 % is something to worry about. I have  
compared Dialux with
Radiance in the past and the results differed by 10-15%. Have you  
double checked your
geometry?


> I have used the folowing gensky and rtrace command in Radiance:
>
> gensky 6 21 12 -c -a 59.9 -o -10.8 -m -15.00 -B 55.866
>
> rtrace -w -h -I+ -ab 20 -aa 0.1 -ad 512 -as 64 -ar 128  
> DF_OfficeLL.oct < DFcoordinates.inp | rcalc -e '$1=($1*0.265+ 
> $2*0.670+$3*0.065)*179/10000*100' > OfficeLL.log

'-ab 20' - impressive! I usually don't go higher than 6. If your  
afraid of missing some
tiny value in the third decimal you should use '-av' to set a  
background value. One
way to find this is described in RwR using rvu, another is to check  
the output of the
gensky program for the 'Ground ambient level' and adjust that for  
your indoor situation
(1-2% of the outdoor level).

If you have a detailed geometry (small windows and openings) you  
should also
increase '-ad' (4096), '-ar' (512) and '-as' (256). The speed penalty  
here is less than
that of an increase in '-ab' so I tend to be pretty bold about these.

I have noticed that Radiance seems to add to your rtrace results the  
higher you
set your '-ab'. I'd have expected the values to approach an upper  
limit where a further
increase makes no noticeable difference. In reality I could add a  
significant percentage
to the DF simply by increasing the '-ab' value. So I assume that your  
extreme
difference might be a result of the very high '-ab' setting.


Regards,
Thomas
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