Forgetting your thoughts on the hollow key word instead
lets look at the different objects here and their properties.
If we took a box, instead of the plane, and assigned it
a refractive ior value. Inside of this box we place a sphere
with the value you ascribed of rgbf 1. As you have
mentioned by itself floating in air the object is technicaly
invisible. When you place the sphere inside the box on the
other hand it would be treated as something akin to an air
pocket inside a glass cube. The rays calculated for the space
in the cube will be different than those for the rest of the box
object. While technicaly this is an invalid model but it suffices
to illustrate the point.
  The hollow keyword is necessary for pov to understand
exactly what is inside and what is out. If you wanted to
place a media inside the box and not the sphere pov gets
confused as to whose surface normal belongs to who. The
hollow keyword sets this conditionaly but has no other effect
on solid objects. In effect the object is really still solid. Only
the way the objects interior is treated is different when media
effects are being calculated.

Ken Tyler

=Bob wrote:

> I think I get you.
> Except for the fact that, what I'm thinking about is, since there is no csg
> taking place and all the objects are set to hollow (meaning the sphere
> hollowness should be unchanged regardless) why then isn't it still just a
> totally invisible object? It ought to be as a container object should be for
> media and not ever become visible when an external object encounters it.
> I remind you of the fact that *all* objects are set to hollow and inversing
> any would still make for all hollow (or is this the thing, hollow turns
> off???). Reason of course being that the outside of any is already hollow
> anyway, and setting them to hollow is like making the entire scene hollow.
> Right? or am I still not convincing anyone?
>
> Message <36660FC3.9D17DED0@Kopp.com>, Nathan Kopp  typed...
> >
> >> // refraction seems to jump into an external object
> >> // which itself does not have an ior
> >> // 98.91, bob hughes
> >>
> >> // when 1 (inverse used) refraction jumps into sphere, 2 does not
> >
> >Actually, this is technically not true.  The sphere DOES have an IOR... it is
> >1.0 by default.  Because this is the same as the air (empty space), when
> >you don't use inverse, you don't see any effect.  However, when you do
> >use the inverse, as Ken mentioned, the camera is inside the water plane, so
> >there is a change in IOR values when the light beam passes from the water
> >(ior 1.23) into the sphere (ior 1.0).  Therefore, POV calculates the
> >refraction angle properly.
> >
> >-Nathan
>
> --
>  omniVERSE: beyond the universe
>   http://members.aol.com/inversez/POVring.html
> =Bob

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