So I'm Driving in the Fog this Morning...
Jason Galterio
Posts: 2,562
...and it occured to me...
I know there are smoke and fog products. I am not going to pretend to understand how they work, but I know that I use the living snot out of most of them.
(My usual go to is the Atmosphere Ball included in TerraDome 3.)
One thing that has always alluded me is the way the fog isn't uniformly the same appearance. This became abudantly clear to me as I was white kuckling it on the highway. The thickness of the fog would be different here and there, in clumps, in drifts, sometimes lower to the ground, sometimes higher...
Is there a way to replicate this effect without using an image plane fog? Maybe by being able to apply some sort of height map or bump map to the Atmosphere sphere?
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I don't have the Atmosphere Ball or TerraDome 3 or know which render engine it uses, but presumably you could use any random image map applied to whatever controls opacity, which would make it thinner in some places and thicker in others. You could paint your own, or in a pinch just pick any random image map that is "foggy" and random in appearance, perhaps one from some other fog prop, or a soft dirt/grime overlay, a bark/fruit texture, etc.
This is with Iray and I've tried that, but it doesn't work. Most likely due to the ball being a globe with depth, not just a skin over a round space.
I'm not sure randomness in Iray volumetrics is supported yet, which is a great shame.
I am not sure that randomness would work either.
There's an organic quality to fog / smoke that would require the denser areas to build off of itself and then feather to disperse. Rather than just be random spots...
It may very well be impossible to do without some sort of particle effects.
I'm not sure, but I think UberVolume (for 3Delight) evidences some randomness in distribution - though it isn't (to mey memory) a wildy varying density.
It's just one of my personal pet peeves....
God rays are usually consistent in their density. But then they are usually seen from a distance and are huge in size.
Fog / smoke in head lights, windows, street lamps are more organic in consistency. Just from being at a closer distance and smaller in size.
Dust would be the exception, but dust in light beams gets kind of boring after a bit.
It's among my list of pet peeves, too. I am sure it will be developed in the fullness of time, but meanwhiel it's a royal PITA
What you are looking for are volumes that have heterogenous density. As you have observed, in the real world, fog (and clouds) has density that varies. Iray currently only supports volumes of homogenous density (like a solid piece of glass or the pure water inside a container). I do not believe there is any great way to get a truly convincing look for fog/clouds/smoke with Iray. If you try to simulate it with billboards all rotated to face the camera you will still have hard edges around the outline of the fog instead of thin, less thick wisps you would see in real life. Billboards also won't react to light the way a real volume would either (self-shadowing as seen as the darker parts of clouds and thick fog, light scattering inside the volume with intensity varying in all directions based on the density).
Probably the best way to get fog/clouds into an Iray render is using a different render engine that does support realistic heterogenous volumes to render the fog/cloud/smoke and then composite it into the Iray render with a compositor like Natron or Fusion.
Very true. I have way too big an investment in DAZ to move to another program. So I have pretty much come to the conclusion that I will never get this functionality.
However, I do have a way around it, even if it is a bit time consuming.
1. Render the image with no dust in the scene at all.
2. Render a second time with the density of dust across the whole scene.
3. Layer both images together in an image editing software.The non-dust image on top.
4. Use the erase function with brushes to erase out the areas where I want the fog to appear.
This ends up with a more organic, less uniform appearance, but is fairly time consuming.
Carrara and Bryce have volumetrics, just saying ....
True. I haven't used Bryce in over 15 years. Use to use it regularly, even used it to make multiple training videos.
But being able to make fog isn't enough of an incentive to go back.