[Radiance-general] REALLY STRANGE

[Greg Ward]

Hello Lucio,

It is normal for rtrace (and other Monte Carlo ray-tracing programs)  
to return slightly different results for the same ray, due to  
randomness in the sampling process.  The goal is to produce the  
correct result on average in a reasonably unbiased estimation  
process, rather than producing the same systematically inaccurate  
result each time, as would be produced by a completely deterministic  
algorithm.

I hope this is helpful.
-Greg

> From: "loscotec\@libero\.it" <loscotec at libero.it>
> Date: December 28, 2007 3:35:34 PM PST
>
> I was working on my thesys and I did have a very strange response  
> form rtrace.. Am I missing something or is it a dangerous bug?
>
> I did cast two times the same call and I did have sistematically  
> two different results.. WHY ?
>
> So I did calculate the same thing from different files:
>
> prova.dat containing :
>
> 2.5 -60 1.5 -1.667 61.1 -1.5
> 2.5 -60 1.5 0 61.1 -1.5
>
> and prova1.dat containing just the second line :
>
> 2.5 -60 1.5 0 61.1 -1.5
>
>
> I did cast the command :
>
> cat prova.dat | rtrace -h- tmp/U0.oct
>
> obtaining :
>
> 5.804947e-03    5.804947e-03    5.804947e-03
> 5.987884e-03    5.987884e-03    5.987884e-03
>
> and
>
> cat prova1.dat | rtrace -h- tmp/U0.oct
>
> obtaining :
>
> 5.996149e-03    5.996149e-03    5.996149e-03
>
> second line of first result, if I'm not wrong, should be identical  
> to second result... Why is it not ?
>
> Lucio Boscolo