Hi Axel,

If the latest binaries are giving you consistent results (you might try 
decreasing the -lw setting when you use -aa 0 to see if you can get those 
results to line up), then I would say the problem is likely the change I 
mentioned earlier (ambcomp.c rev 2.73).  The new Hessian code has to avoid 
coincident (or nearly coincident) ambient samples, and the code I originally 
wrote for this introduced some serious bias to the calculation that would show 
up for some scenes.  Yours is probably a good test case.  The newer code is 
much more robust and doesn't have this bias in it, so if it is giving you 
consistent results, then you're probably OK.

The thing I worry about is if you get different results with the current code 
depending on whether you use the ambient file.  If your other settings are high 
enough, this should only affect run-time, not accuracy.

Cheers,
-Greg

> From: Axel Jacobs <jacobs.a...@gmail.com>
> Date: April 6, 2018 8:24:20 AM PDT
> 
> Hi Greg,
> 
> Thanks for your thoughts.  We did clean out the old ambient files.  In
> our ADF script, mkillum is run with -n 80 (our servers have between 64
> and 88 virtual processors)
> 
> With -aa 0, the results are on average 32% lower, compared to the 16%
> reduction I mentioned before.
> 
> I was re-running different options over the last few days to get to
> the bottom of this.  Re-running an identical copy of the folder and
> with the same settings that allowed me to reproduce the results from
> Sep (with the old binaries) does now give the same 16% reduction as
> all other combinations of options.  I'm rather puzzled.  It seems as
> if using the old binaries but otherwise identical settings does not
> reliably give me the old results.
> 
> I'm hoping that this is not dependent on the server load, which will
> be nearly impossible to track down.  In the latest runs, loading the
> server to roughly 100% give the same results (16% red.) as loading it
> to 400%, i.e. running the same assessment in four different, identical
> directories.
> 
> I'll run a few more tests next week, and will report back.
> 
> Have a lovely weekend
> 
> Axel

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