David Given <dg### [at] cowlarkcom> wrote:
> So I've got this planet.

> - There's an occasional rendering artifact in the clouds --- which,
> annoyingly, you can't quite see in the low-level scene. Thin
> longitudinal lines trace the shape of the cloud. I assume this is a
> sampling issue, but I don't understand how the adjustments work. Does
> anyone have any advice?

You are correct that this is a sampling error, but we would have to see your
media code to help you correct it.  This is generally caused by too few samples
or low quality samples.  I saw the atmospheric code down there, you should leave
intervals at 1 for method 3.  Intervals greater than 1 is only really needed for
methods 1 or 2.  If your clouds media is in a different container shape, test it
without the atmosphere and see if there is a marked difference.  There is a bug
with the samples value of the first media container hit by rays being
inappropriately reused.  This can cause your results to be very different from
different views.  I recommend making the samples value the same or very close
for both medias.

Try increasing the confidence and reducing the variance, and try raising the
samples.  If the patterns are fairly subtle, a small amount of jitter can help
break up the regularity for minimal speed penalty (depending on your aa
settings).


> Incidentally, the clouds take an absolute age to render. The
> high-altitude picture took 20 minutes, with antialiasing on. An 800x600
> version takes about six hours. Given that my scene contains precisely
> four objects, not including the sun, I'd like to put in a bid for the
> Least Efficient Scene prize...

Scattering media is slow, but can be optimized.  Make sure medias with complex
densities fit their container shape as tightly as possible.  Be careful about
boosting the aa values too high - I rarely see much improvement over 5.  I tend
to stick with 4 for most finals, and use 2 or 3 for testing.


HTH,
-Reactor

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