"Chris B" <nom### [at] nomailcom> wrote:
> "JEofVA" <jce### [at] attglobalnet> wrote in message
> news:web.486a9b1613f6a9318a187d850@news.povray.org...
> > As the Subject says, I'm very new at this, and not sure what I'm doing
> > wrong.
>
> Welcome to the newsgroup.
>
> > The image I am trying to render is one of a sphere of nested multi colored
> > spheres with a wedge removed to reveal the inner layers. I get what I
> > think I'm
> > suppose to get, except the inner spheres are speckled with lots of black
> > pixels.
>
> This sounds like a very similar problem to the one discussed a couple of
> weeks ago in the thread
>
http://news.povray.org/povray.newusers/thread/%3Cweb.48513efe78241c82b979a58c0%40news.povray.org%3E/
>
> >
> > I read the piece about coincident surfaces causing this effect, but if
> > that is
> > what the problem is, I don't know what surface needs moving.
> >
>
> I think it is indeed coincident surfaces. The cut surfaces of your Crust,
> Mantle, OuterCore and InnerCore all align exactly.
>
> Two alternative solutions are mentioned in the thread above. One is to
> 'difference' the next smaller sphere from each larger sphere (Subtract the
> Mantle sphere from the Crust, the OuterCore sphere from the Mantle and the
> InnerCore sphere from the OuterCore). The second is to just have one sphere
> and use a color_map to give the shells different colours.
>
> In this case there is also a simple third option and that is to move the
> corner of the box that you are using to slice out the segments. If the Crust
> box starts at <0,0,0> you can use 0.00001*<1,1,-1> for the Mantle box,
> 0.00002*<1,1,-1> for the OuterCore box and 0.00003*<1,1,-1> for the
> InnerCore box. This tiny difference is enough to make sure that the cut
> surfaces are no longer coincident.
>
> Regards,
> Chris B.

Chris,

I tried your "simple third option" and it worked.  I'm still not precisely sure
why it worked, but I will mull it over until I get it.  I understand what you
did, just not how it made a difference.  I guess I'm not fully understanding
this coincident surface thing.

But, thank for the help... oh, and I'll try to remember not to write below my
signature from now on.

Jonathan
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