"scam" <sca### [at] mailusydeduau> wrote:
> Hi all, could someone run the code below and tell me if they see large
> artifacts?

I'm coming late to the discussion, sorry.  I was testing out your code,
which is a good one for producing these artifacts. This is a problem I've
been giving some thought to lately as well.

On my own system (a Pentium II 400MHZ, running Windows version of POV-Ray v
3.6.1) I'm actually seeing artifacts at MOST values of myscale -- the only
artifact-free "zone" I can get is from 0.5 down to 0.013 --and then CRAZY
artifacts from 0.0127 on down (possibly floating-point errors there? All
the scene's values are very small in that domain, and the camera is getting
quite close to the origin and your object.)

Yep, it does seem like a bug.

I have a theory: From a purely visual analysis of your scene, it seems that
the artifacts are at their worst when the camera is perpendicular to the
sphere sweep object (or its points.)  That is, imagine each point in your
sphere_sweep having a plane slicing right through it from front to back, at
right-angles to the surface there. Like a knife blade slicing the
sphere_sweep into perfect tube segments at each point. If the camera
happens to be looking RIGHT AT those imaginary planes, edge-on (as in your
scene), it sees the most artifacts. Moving the camera off-axis of those
planes (all of them, not an easy or practical thing to do) eliminates most
if not all of the artifacts. That's borne out by experimentation I've done.
Which could also explain something I've noticed in my own scenes, why longer
sphere_sweep objects tend to show more problems: There are more points--and
thus more imaginary planes to have to avoid.  Close to impossible to do, of
course, with a long, sinuously curving sphere_sweep object. What's
surprising (to me) is that an orthographic camera shows the artifacts in
your scene in a different way--no longer as radiating spikes. So my theory
could be wrong. But it does help me in trying to understand what's going
on.

Ken W.

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