On Mon, 18 Jan 1999 02:37:53 -0800, Ken <tyl### [at] pacbellnet> wrote:
>Ken wrote:
>
>> On a recent scene I was working on ( see povray images "If you can't go
>> to heaven") I was using media inside of a plane. I could only see the media
>> when the camera is inside the plane and not while outside. Why ?
>> The plane used is at y*0 with the camera at y*-2 using planar for the
>> density type. If I put the camera at y*2 or even y*20 with the look_at
>> at y*-10 to make sure I'm pointed an the surface of the plane the media is
>> still invisible in the scene.
>>
>> --
>> Ken Tyler
>>
>> tyl### [at] pacbellnet
>
>Perhaps Ken it is because a plane is not a closed container ?

That's about right.  For fun, try putting another object inside the
plane. Then you'll be able to see media from outside the plane, but only 
in the places where the ray ends up hitting the other object (even if
the object itself is completely invisible.)  

POV only calculates media effects along a ray after it determines the 
exit point for the ray.  Planes, being infinite, tend not to have exit 
points unless the ray enters another object or starts from inside the 
plane.  (And not all rays that start inside the plane have exit points:
try pointing your camera parallel to the plane when it's inside for 
another weird effect) To fix this, you might try adding another plane 
with the same normal but situated below the plane you're working with, 
or you might try using a large box.

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