In article <3fa9a7ef@news.povray.org>, Warp <war### [at] tagpovrayorg> 
wrote:

> Matthew Pace <mat### [at] lycoscom> wrote:
> > 1) Wouldnt just a plane show up?  y equals 0 on only one plane, doesnt 
> > it?
> 
>   By default POV-Ray will take any point which is *inside* the isosurface
> as the surface of the object. This means that if the surface of the
> container object is inside the isosurface, it will show up.
>   You can use "open" to stop it from doing this.
> 

Oh ok, thanks, I should have guessed...

> > 2) If y is negative, why is the positive part of the sphere shaded?
> 
>   Because it makes the check -y<0, which is the same as y>=0.

And that makes sense too, because what is inside a function is generally 
considered to be true too.  Thanks.  Last question:  is there a way to 
make it so that it is function=threshold?  Thanks

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