[Radiance-general] Ambient Bounce parameter recommendations/studies

[Lars O. Grobe]

Hi Judhajit!

In addition to previous replies, I would recommend these two:

1) study how rad is setting the ambient settings based on the 
information given in the rif-file - it is usually quite successful doing 
so. Code is open source...

2) Mark Stock did a lot of experimentation, especially focusing on 
scenes with large amounts of geometry objects which tend to stretch the 
ambient cache's efficiency. He was especially interested in rendering 
times and the visual appearance, still a great documentation by Mark at

http://markjstock.org/radmisc/aa0_ps1_test/final.html

Besides that - it is good practice to do some work on finding out when 
you settings lead to "stable" results. So for each scene type, it may be 
wise to vary ambient settings from "high performance" to "high accuracy" 
for different ambient bounces (-ab), at least once for sunny and once 
for cloudy skies. You can do so e.g. by rendering illuminance on the 
floor plane one pixel wide perpendicular to the facade. Plot the 
results, and you will find

a) at which number of ambient bounces increasing -ab does not lead to 
significant increase in recorded illuminance

b) at which "accuracy" you get a reasonable (usually rather smooth) plot 
- very low accuracy tends to give a lot of spikes in such a plot, even 
if the average may be acceptable

Having these tests done will probably give you a much better feeling 
about the parameters in your rpict/rtrace command line and should be 
kept with the results :-)

Cheers, Lars.