William F Pokorny <ano### [at] anonymousorg> wrote:
> Documenting long standing exposures with the sor tutorial example.
>
> Ref:
>
>
https://wiki.povray.org/content/Documentation:Tutorial_Section_3#Index_Entry_sor_tutorial
>

[running v3.7.0 and 3.8 beta 1-- the results are essentially the same]
Windows 10

I ran a lot of animation tests, moving the scene elements around in relation to
one another, and this is how the situation appears to me when using 'sturm':

1) For the OUTSIDE surface of the SOR that *faces* the light source (whether or
not 'open' is also used):
     sturm OFF: lots of noise and artifacts
     sturm ON: no noise that I can see

2) For the 'open' INSIDE surface, in the *shadow* areas:
     sturm OFF: no noise that I can see
     sturm ON: lots of noise etc.

So I wonder if the problem is just shadow artifacts: sturm on/off has the
opposite effect on the inside and outside-- and on the lighted surface vs.
shadowed surface(!)

The appearance of the noise and the artifacts on the *outside* depends on the
the camera position, its look_at point, the position of the light(s) and the
orientation of the SOR-- all of which interact, unfortunately. It looks the
worst to me  when the y-positions of all three are the same (and not just when
the camera is looking straight into +z).

Since the SOR when 'open' is really just an infinitely thin shell, it seems to
me that using it this way is not a good idea anyway, as  the walls have no
thickness at all and look unrealistic. (The docs also mention that it shouldn't
be used in CSG this way.)

(BTW: I tried using 'inverse' in the SOR, just to see if it made any difference
at all. It does not.)

I'll follow up here with a few of the test animations I made.

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