[Radiance-general] Deterministic calculations with Radiance

[Gregory J. Ward]

Hi Chris,

If you turn off all stochastic processes in Radiance, you get the worst 
imaginable results.  I don't think there's any way to get repeatable 
output from Radiance that isn't terrible.  To see what I'm talking 
about, try compiling with the -DNORANDOM flag.  Even with this flag 
set, the results will be hypersensitive to small changes in 
illumination values, etc., as the decision on whether to trace 
particular rays may be go above or below the threshold.  The only way 
to avoid this is to set -lw 0 and rely on the -lr parameter to end 
recursion.

The ideal approach would be to use a pseudo-random number generator 
that is repeatable.  In principle, Radiance does this, but due to 
differences between machines and implementations, in practice it does 
not work out that way.

-Greg

> From: Christopher Kings-Lynne <chriskl at familyhealth.com.au>
> Date: February 2, 2005 5:13:27 AM PST
>
> Hi,
>
> I'm thinking about setting up automated regression testing for my 
> Radiance application.
>
> Now, the problem is for these I wish to make Radiance run 
> deterministically, so that I can run diffs of output against known 
> good output, etc.
>
> Is there a way of doing this?  Do I need to set a bunch of jitter 
> arguments to 0?
>
> Cheers,
>
> Chris