Brian,

Thanks a lot.  That's really good to know.

I'd appreciate your input, if you don't mind.  I'm getting ready to launch into
a new round of gem experimentation. (I started with the planes, then tried boxes
and had the problem I started this thread about.)  I'm thinking about using a
mesh object to attempt a more complex and more extensively faceted gem.  Do have
any thoughts or warnings you'd care to share as I get ready to attempt this?

- Patrick

Brian Elliott wrote:

> "Patrick Hagerty" <pat### [at] daeoriaorg> wrote in message
> news:43655054.BFA2ECB2@daeoria.org...
> > OK.  I tried it.  It worked.
> >
> > I was simply failing to think in three dimensions.  A plane is two
> > dimensional,
> > a box is three dimensional.  That's what I get for doing most of my
> > POV-Ray
> > work in the evening after a day of mind numbing work.
> >
> > Thanks again.
>
> Hello Pat,
>
> Not meaning to be a pain, and it doesn't impact your gem solution, but just
> to explain pedantically in order to be safe...  In PovRay's Constructive
> Solid Geometry, a plane is considered a 3-Dimensional object - ie. like a
> box, the plane has an inside and an outside, except the inside of a plane
> extends infinitely.  A triangle or polygon, however is two-dimensional - it
> has no inside nor outside.
>
> If you invert the normal of the plane, eg, from y to -y, the plane will look
> identical, however "inside" and "outside" are reversed.  This will make a
> big difference to the behaviour of unions, intersections and differences.
> It also impacts on media.
>
> Cheers,
>    Brian

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