I have a scene I'm working on which involves a hall in an old building. 
Early in the morning golden light streams through the eastern windows. 
The dust in the room is caught in this light and shows the beams of 
light as they cross the room.

I'm trying to model these beams. I have the light worked out, and I'm 
playing with media, however I can't get it to the point where it's 
(nearly) invisible anywhere else and shows up as a haze where the light 
hits it.

Any help greatly appreciated.

The interior of the room comes from this attempt:
//dust in the room
box {
	<-5,0,-3.0>
	< 5,6, 3.0>
	hollow
	pigment { rgbt 1 }
	interior {
	media {
		scattering { 5, <0.1,0.08,0> }
	}
	}
}

But this results in a fairly even yellowing of the room. (I've tried 
scattering 1 .. 5 with similar results)

I've attached a render of the room (no AA) using the above media and 
without the media.

Cheers!
Rick Measham

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Attachments:
Download 'nochnodust.jpg' (37 KB) Download 'noch.jpg' (76 KB)

Preview of image 'nochnodust.jpg'

Preview of image 'noch.jpg'

> But this results in a fairly even yellowing of the room. (I've tried
> scattering 1 .. 5 with similar results)

First, use scattering 1 until you get the effect you're looking for.
Changing parameters wildly won't help you out with this sort of problem;
it's likely to just confuse matters.

It looks like you're actually getting the effect that you're asking for, but
it's so poorly sampled that it looks very ugly, like there are window-shaped
yellow things hovering in the air. If you turn up the sampling parameters
then it will probably look right.

Try adding

samples 100

to the media block. If that still doesn't look good, bring it up more. If it
looks great but is too slow, try bringing it down. You want the lowest value
that looks good. You might want to render with +SP16 in the command line to
get a quick preview of the image without rendering every single pixel, since
this may slow things down.

If you really want it to be "invisible anywhere else," then also use
"extinction 0" in the scattering block to turn off the absorption that
occurs everywhere (though you may not want to do this since dust does absorb
light).

 - Slime
 [ http://www.slimeland.com/ ]

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