[Radiance-general] Setting ambient accuracy (-aa) to 0

[Kam Shing Leung]

Dear all,
 
I intend to model the amount of solar radiation falling onto different parts of a building facade.  To do this, RTRACE is used.  An array of measurement points at 1-unit interval is assigned on the facade.
 
To model it properly, I am currently deciding on the ambient settings.  My understanding is that, by setting -aa to 0, there will be no interpolation of irradiance values, and so all the backward ray-tracing will be conducted exactly at the measurement points.  But I also read an advice aganist turning -aa to 0 for the purpose of evaluating irradiance value in a space (see the thread below).
 
Could anyone advise whether it is appropriate to set -aa to 0 in this situation?  Corrections on any misconception of mine are also appreciated.  Thanks!
 
Cheers, 
Kam
  
 
Gregory J. Ward gregoryjward at gmail.com 
Thu Dec 28 22:04:38 CET 2006 


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Just wanted to chime in on this thread.  The -aa 0 setting is  
appropriate when you have a lot of small geometry that isn't safe to  
leave out of the ambient calculation (using the -ae or -aE options),  
or for special applications such as mkillum or rtcontrib.  Turning  
off the ambient cache is NOT a good idea when what you care about is  
individual ray accuracy, such as when you are using rtrace to  
evaluate radiance or irradiance values in a space.  It can be done  
with -aa 0, but you have to pay close attention to your other  
parameter settings (such as -ad, -as, -lw, and -lr) and alter them  
appropriately.  The -ar setting has no effect with -aa 0.  Ditto for - 
aw.

-Greg



      
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