Atmosphere and Background node question

Hetzen · July 18, 2009, 08:52:22 AM

I'm watching my GI pass on a render, and I've deliberately set the atmosphere up to 480. As you can imagine, it's taking a while to work out. Now, without stopping the render, I'd like to ask this question.

Can I get the atmosphere to only work on my objects if I turn the Background node off?

The thing is, is that my scene is in a snow white-out looking up, so there would be no need to work out what the sky is doing. I'm just interested in getting a thick atmosphere around my imported objects.

Any ideas?

Cheers

Jon

Henry Blewer · July 18, 2009, 09:02:13 AM

I think I would have used a cloud, as haze (fog), set to the colors you want the atmosphere to be. Do clouds render without an atmosphere?
In Lightwave or Blender, you add mist (fog). Terragen 2 does not work the same way.

Hetzen · July 18, 2009, 09:11:25 AM

Scratch that. Doesn't work.

Henry Blewer · July 18, 2009, 03:45:12 PM

Hmm... I still would go with the objects being inside a cloud used for fog.
I'm stuck. Sorry.

PG · July 18, 2009, 04:05:21 PM

You can't disable the background object but to be honest there's no reason to. It's only a big inside-out sphere. You can still disable the atmosphere node but everything'll go monochrome. You can also turn off the primary and secondary independantly. Don't think they'll do much for performance though.

Hetzen · July 18, 2009, 04:47:20 PM

Thanks for the suggestions. The reason why I don't think the cloud approach would work, is that I have a bright light source generating a glow in a thick atmosphere, and only need the atmosphere around the light and the shadow of my imported geometry and not in the sky (which there's a lot of). But then saying that, does the cloud node work in the same way as the atmosphere in terms of adding a form of volumetrics to a light?

Matt · July 18, 2009, 08:51:19 PM

You might try reducing the atmosphere's "Ceiling" value so that's only slightly greater than the altitude at the tops of your geometry. The atmosphere will stop abruptly above that. You could then use less atmosphere samples (because the distance between samples is based loosely on the distance between the Floor and the Ceiling).

To make up for the lost atmosphere, set the background colour of the background sphere. You'll want the background sphere to contribute to GI, but I think it only contributes if you reduce its radius to quite a lot less than its default, so you will need to do that. Try -1e7 (keep the minus sign).

Matt

Matt · July 18, 2009, 08:55:16 PM

Quote from: Hetzen on July 18, 2009, 04:47:20 PM
Thanks for the suggestions. The reason why I don't think the cloud approach would work, is that I have a bright light source generating a glow in a thick atmosphere, and only need the atmosphere around the light and the shadow of my imported geometry and not in the sky (which there's a lot of). But then saying that, does the cloud node work in the same way as the atmosphere in terms of adding a form of volumetrics to a light?

Yes, you could try disabling the atmosphere altogether and just use cloud layers where you need them. They respond to light in a way very similar to the atmosphere, most of the things that work in the atmosphere also work in the cloud layer (except for settings particular to one or the other).

Hetzen · July 18, 2009, 09:19:28 PM

Thank you Matt, that's good food for thought to digest. At the moment I'm doing a proof-of-concept as a still, which may well turn into an animation, in which case a mixture of the atmos ceiling on top of the cloud concept would make frame renders do-able. I've set a 3hr render time as a cut-off on HD resolution. The GI pass at the moment is 2hrs, so any shaving on that would really help the future of this project, however a long shot it is already.

Hetzen · July 18, 2009, 09:30:54 PM

As another question, could you set up several Atmosphere nodes in a chain with different ceilings? ie, is the input on the atmosphere node active?

buzzzzz1 · July 18, 2009, 09:35:51 PM

Quote from: Hetzen on July 18, 2009, 09:30:54 PM
As another question, could you set up several Atmosphere nodes in a chain with different ceilings? ie, is the input on the atmosphere node active?

Hope you mind my jumping in? But I have a render going where I wanted normal height haze and low level ground haze. So I fed another atmosphere into the input of the existing and set the 2nd atmo to low level, and it works so I would have to say yes. Hope this answers your question.

Hetzen · July 18, 2009, 09:41:34 PM

Certainly does Buzz. Thanks for chiming in.

Henry Blewer · July 19, 2009, 08:28:08 AM

Thanks Matt. This renderer has some real power. Being able to turn off the atmosphere, but still use clouds... More flexibility. I could be possible to render a terrain inside an object. Like those snow globes you shake up.

Henry Blewer · July 21, 2009, 03:18:15 PM

I added this low cumulus cloud layer to simulate fog. I forgot to turn on ray trace shadows before I went to work.

Is this something like you are interested in?

http://farm4.static.flickr.com/3443/3743775110_6605f3eacb_o.jpg

I kept the fog/clouds below the tree tops; a it shows what I was thinking for your question, and b the sun is blocked from burning it off as quickly.

Hetzen · July 22, 2009, 08:40:31 AM

Thanks njeneb, nice scene you've got going on there. I was thinking of something a lot thicker, but see the process is something to explore. Cheers