"Burki" <nomail@nomail> wrote:

>
> Any idea how to get rid of the silly dots on top of the stela?

This is quite a thorny little problem!

Spent several hours with your code, trying just about every conceivable
combination of things, eliminating this, tweaking that, moving the object
here and there, yet the problem wouldn't go away.

Moving the camera around, I could see that the dark areas were confined to
the rounded edges of the shape and nowhere else (but visually distorted by
the high IOR to appear as odd blobs and speckles, at odd
locations...depending on where I placed the camera.)

So I added a sky_sphere, with a single gray rgb .5 value, and that DID
eliminate most of the problems (as has already been noted.)  Well, the
major dark areas were now "filled in" with gray (filtered by the cube's
redness, of course), so they blended better with the rest of the shape's
colors. But SOME actual dark areas still remained, at the object's "edge
centers."

I began to think that the problem had something to do with your scaling of
the object--that its IOR was also being scaled in some weird way,
non-uniformly.  But reading the POV docs, IOR isn't scaled (nor is anything
else in an INTERIOR block.) Eliminating your interior's light fading didn't
help either.

In frustration, I replaced your isosurface object with a regular, non-scaled
superellipsoid, as you did...which also didn't help.

Thinking your plane's marble texture was contributing something odd,  I
changed it to a simple rgb .5 value.  STILL no good.  Eliminating the
object's shadow didn't help either. MADDENING!

(In my frustration, I even began to imagine that the problem might be
lightwave interference inside the object...one wave canceling out another
and creating dark areas. But POV doesn't use "lightwaves".)

Since the MAX max_trace_level of 256 was now being exceeded, I was ready to
give up, and blame the problem on that.  (BTW, if you plug in a really high
max_trace_level value, POV simply limits it to 256... something I didn't
know until now. So 1000000 or whatever is the same as 256.)

Then it dawned on me: Your scene's lights are spotlights...which means,
somewhere outside the scene's visible area, the plane was going to
near-black, outside the spotlight cones. So I changed the plane's finish to
ambient 1 diffuse 0 to eliminate the lights' effects, and VOILA!!  The
remaining "problems" disappeared!! Your original object was just picking up
those remaining dark areas and distorting them into unrecognizable shapes.
And even though max_trace_level was being exceeded (with my "simpler"
superellipsoid), I couldn't see any trace of that.

Of course, now my superellipsoid justs looks like a big red cube!  Nothing
of visual interest outside it to give its IOR something to work with. So it
does needs *something* darker or brighter outside, to show its optical
effects...which may end up looking like artifacts.

This was a fun little scene to play around with and learn from.

Ken

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