Vray Light Fog

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  07 July 2013
Thumbs up Hi

I saw your thread the other night, and you are not alone.

Here are some links that I found on the subject -

Mostly a max/xsi user myself

http://www.peterguthrie.net/blog/20...-museum-take-3/

http://www.fourdimensions.co.uk/wordpress/?p=499

http://cgworkshop.org/forum2/showth...nd-Vray-Fog-%29

The links work based on vray although since you are in maya- but I'm sure you will find their equivalent.

Drove myself nuts for a while sometime ago DIY
( without just stopping to look for reference)
but these seem to be the most spot on- but that's just my take on it.

they may be of some help.

gl.
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Last edited by burntheskies : 07 July 2013 at 07:38 PM. Reason: append
 
  03 March 2014
was just looking for something else in regards to vray and fog and noticed that this post mentioned the fog density is capped at 1.

You can make it go higher than the UI limits if you create an expression, right click it and create VRayEnvironmentFog1.density = 10;
and render, for maya 2014 appears to get denser.
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  03 March 2014
I could be wrong, but couldn't volumetric fog also simulate dust particles being illuminated, and not just water vapor? In which case, the IoR would be different perhaps, but obviously the visual effects appear similar, often. Depending on the dust medium - gritty, dirty, or sandy dust would be kind of a different story. But not the same optical or physical effects.

One problem from the programming end of this, and why I imagine it's so difficult for any rendering engine to reproduce accurately, is the gigantic fudge that is Rayleigh scattering. It doesn't work to explain our own atmosphere and sky, and I would guess that when the coders plugged this in to their rendering engines they realized this and had to go with some other mathematical fudge to get anything to resemble what we see in real life. This is of course true with all atmospheric math, in all the applications and renderers, but likely becomes much more evident when we get to volumetric lighting and sunbeams.

I digress (of course), but I'm about to finally switch over to Vray and it's key to know what limitations still exist, if any. Volumetrics won't kill my decision in this case.
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  03 March 2014
The only raytracer that handles volumetrics and fog easily&fast is Arnold. Actually it handles volumetrics easier and faster than any renderer I've seen. Glass&caustics renders slow in Arnold, but throw in and combine anything else and it doesn't slow down.

Anyway. To get those tiny reflecting particles in volumetric lights and beams you either would need to fake them entirely in post, or would need to build a dense particle field in your 3D scene. (Preferably making it only show up in the cone region of a spot light)
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  05 May 2014
Hello

-Panupat I will have to try this
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  10 October 2015
What a juggling act. You can't take a nicely lit scene and simply add fog to some of the lights - you have to re-set all the light intensities in the entire scene all over again, and by different amounts depending on what type and what brightness they are. Then if you're disatisfied with the fog density and change it ( or a supe tells you to change it), you have to adjust every single light intensity all over again.

I appreciate the realism, but that's not flexible enough. It's like forcing us to use both diffuse and reflection for every light all the time, for the sake of realism.
 
  10 October 2015
For the record, mental ray is no better, with or without volumetric lighting. It's about as predictable as an asshole on your elbow. Why? Because the fundamental light equations are wrong, as I've been saying for years. Maxwell was close, but even he couldn't separate light in his equations.
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  10 October 2015
hi

the light / rendering / precalc part of all of this can be like * juggling a bunch of saws while standing on a net of rope. one adjustment and the whole things fails but it is improving. After spending years grinding towards a perfect beauty right in the viewport without any post- its safe to say post almost always wins. There should however be a way to render these types of physical phenomenon with current available computer strengths. Arnold is great although can get a little hungry at times with my machine resources.

What about precalc GI ? the moment you move your lights its the same story anyway- so in those cases the workflow is very linear. I don't know of any people go in and merge their IRmap/LCmap passes together manually, they just say screw it and recalculate the thing.

Hope i'm not wrong in saying this.
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  10 October 2015
Originally Posted by InfernalDarkness: For the record, mental ray is no better, with or without volumetric lighting. It's about as predictable as an asshole on your elbow. Why? Because the fundamental light equations are wrong, as I've been saying for years. Maxwell was close, but even he couldn't separate light in his equations.

Good to know, thnx

Quote: safe to say post almost always wins.

Assuming you're a 2D effects artist, sure. Have you ever done an animated volumetric light, that interacts with other 3d objects, in post? I know a little bit of comping, but I have no idea how that's done - I'm sure they'd need to bring 3d geo into nuke. All that extra knowledge and time required for something that a supe would ask for just on a whim -

Quote: What about precalc GI ? the moment you move your lights its the same story anyway- so in those cases the workflow is very linear. I don't know of any people go in and merge their IRmap/LCmap passes together manually, they just say screw it and recalculate the thing

Baking is a whole different subject - if you bake something, then change it, of course you have to bake again! Having to re-light your scene just to add one lighting effect though, that can be a no-go, and I'm not going to use it at all now.

Seems to me all that's needed is voxels contained within the light's frustrum - but, no, I'm not going to claim to be even half as smart as vlado or other render programmers - and who knows, maybe it's just not a high priority.
 
  10 October 2015
re:

Originally Posted by guccione: Good to know, thnx

Assuming you're a 2D effects artist, sure. Have you ever done an animated volumetric light, that interacts with other 3d objects, in post? I know a little bit of comping, but I have no idea how that's done - I'm sure they'd need to bring 3d geo into nuke. All that extra knowledge and time required for something that a supe would ask for just on a whim -.


Yes, I actually have- and yes it became a nightmare after a while. With opacity mapped tree leaves no less and the camera was crossing line of sight for the sun source. It was actually part of the reason for my posting at the time. Would I risk that with what I didn't know about rendering this effect in a production environment- probably not likely. These days though if I had the time for a personal project I'd say exploring deep could be a possibility.

Originally Posted by guccione: Baking is a whole different subject - if you bake something, then change it, of course you have to bake again! Having to re-light your scene just to add one lighting effect though, that can be a no-go, and I'm not going to use it at all now.


Also correct. I was trying to be relative- but I did leave of the focus of the post. On another note if the light effect is purely additive like "gods rays", it is possible to do that with post and not having to relight the scene.

Originally Posted by guccione: Seems to me all that's needed is voxels contained within the light's frustrum - but, no, I'm not going to claim to be even half as smart as vlado or other render programmers - and who knows, maybe it's just not a high priority.


Maybe point cloud geo can do what we can't figure out in this way? Hey I'm just glad the post is coming alive and well- rendering always had its lions share of problems.
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Last edited by burntheskies : 10 October 2015 at 10:45 PM. Reason: multi quote
 
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