Thanks for all the ideas, guys. I'm new at this, so I'm not quite sure how
to use the macro - how do I use the point it returns as the position for
the spheres?

Also, The reason I'm using a cone (which is situated so the axis is
perpendicular to the line of veiw) is because the main belt actually
stretches from about Earth's orbit out to Jupiter, with most of the
asteroids between Mars and Jupiter. I'm trying to give this impression with
a cone, so that the narrow point (at earth) has a few asteroids, and then
the broad part of the cone is in the "belt" itself, between Mars and
Jupiter.

Thanks again!
OpPl

"Bill Pragnell" <bil### [at] hotmailcom> wrote:
> Alain <ele### [at] netscapenet> wrote:
> > In fact, a long cylinder, possibly flatened, would be a good aproximation in
> > most closeup cases. The cone can be used to produce a kind of forced
> > perspective, but then, you need to adjust the scaling of the asteroids to the
> > radius of the cone at the asteroid location.
> Ah yes, I get the idea. I'm too much of a physical purist! (So I won't even
> mention the mean separation of asteroids in our own belt... :)
>
> If you don't mind a slower render time, you could use an isosurface. Take a
> pigment function like crackle, then vary the threshold (as a constant in
> the function {} block) as 1/r or something similar, where r is the distance
> from the cylinder/cone's axis.
>
> For a sphere, you end up with something like this:
> http://www.infradead.org/~wmp/gallery5/iso1.jpg
>
> Of course, the threshold here goes from 0 -> 1, so cut it off to leave the
> rocks spaced out at the centre.
>
> Bill

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