I use the -aa setting to get a smoother indirect calculation. This is especially important if the -ad parameter is low, i.e., <=512. A high -aa parameter, such as 5000 or whatever, creates a dense grid of indirect/reflected values. You can check that by making two images, one with a low setting of ad and aa, and one with a low setting of ad and a high setting of aa. That will show you immediately what the ambient accuracy parameter is about. The image contains less blotches.
Martin Moeck
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-----Original Message-----
From: [email protected] on behalf of Marija Cvetkovic
Sent: Tue 12/26/2006 2:30 AM
To: Radiance general
Subject: [Radiance-general] ambient accuracy parameter
Hi,
I've been reading some previous posts related to ambient parameters
settings and I have some questions.
When it is recommendable to use -aa 0 value? If I understand this
parameter well, 0 value turns off irradiance caching, so we can use it
when caching isn't needed (mkillum calculation for venetian blinds or
rtcontrib).
When we set -aa 0, does -ar have influence on minimum sampling distance,
since: min sampling distance = max scene dimension* aa/ar.
When I run a rtrace calculation with -aa 0, calculation time is much
shorter than with -aa 0.1. Why?
Have a nice holidays 
Marija.
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