Atmospheric Visibility and Smog

[PabloMack]

I did my first simple render and it brings up questions about the atmosphere.  Quite an interesting effect how the air looks dusty as it scatters more light as the distances through the atmosphere increase.  Reminds me of a small commercial jet ride in 1997 through northern Namibia where there was a thick dusty layer emanating from the desert below that looked like smog in that it had limited height.  We flew above it and visibility was quite a bit better at the higher altitudes.  Is there a way to control atmosheric visibility or "fog density" in TG2?  It would be great to create a map of fog defining its area of coverage (and color) that could also delimit an altitudinal profile of its density.  The light that is scattered can be changed by the composition of the particulate matter suspended in the air.  In the case of northern Namibia, it was a dirty brown color.  Very interesting to see the interplay between suspended particulate matter and the filtering effects seen at dawn and dusk reminiscent of a Dopter shift (though a different mechanism is going on here to cause it).  I tried to find a photo showing this but I guess I never took one.  Who thinks to take a picture of smog? 

[Henry Blewer]

I use a cloud layer for fog effects. This could be image masked or just hit random until the cloud looks about right. Being lazy, I use the random method.

[PabloMack]

Snooping around in the Atmosphere Tab I found the Haze controls which should addresss the issue I brought up in this thread.  The "Haze horizontal colour" under the "Main" subtab seems to control darkness, not color.  I see no way to make it brown, only gray levels.  "Haze exp height" under the "Height control" subtab seems to control the boundary between the haze layer and the clearer blue sky above it.  As for how sharp the gradient is during the transition, I don't see a control.  Also, "Hase glow amount" and "Haze glow power" are things worth exploring.  Probably useful in simulating the haze catching and scattering light near dusk and dawn when the ground is not receiving direct sunlight.  Seems like raytracing should handle this but that might be more expensive.  A true glow might be useful in science fiction scenes where the atmoshere itself might actually generate a luminescence of its own.  

[cyphyr]

If you need a very distinct "cut off" line between your differing densities of atmosphere try njeneb's solution or add a seccond atmosphere and restrict its height to match your "cut off" point.
Richard

[Tangled-Universe]

Snooping around in the Atmosphere Tab I found the Haze controls which should addresss the issue I brought up in this thread.  The "Hase horizontal colour" under the "Main" subtab seems to control darkness, not color.  I see no way to make it brown, only gray levels.  "Haze exp height" under the "Height control" subtab seems to control the boundary between the haze layer and the clearer blue sky above it.  As for how sharp the gradient is during the transition, I don't see a control.  Also, "Hase glow amount" and "Haze glow power" are things worth exploring.  Probably useful in simulating the haze catching and scattering light near dusk and dawn when the ground is not receiving direct sunlight.  Seems like raytracing should handle this but that might be more expensive.  A true glow might be useful in science fiction scenes where the atmoshere itself might actually generate a luminescence of its own. 

I think you're missing a few things?

Haze exp height = gradient control
Haze glow amount/power = a way to generate luminescence of its own (glow amount regulates distribution of glow)
The haze/blue sky colors = not gray levels only, you can make it any color you like

More on-topic. I'd go either for a low level cumulus with a lot of coverage or set the haze density >4 and set exponential height quite low (<1000m for starters). Depending on your camera-height you should be able to see a kind of mist.

[Hetzen]

Interesting discussion. I recently wanted to use some data to define northern europe, for me to the fly down to the Thames in the UK. The problem I was getting, was defining an atmosphere that didn't obscure the land below, yet still give me a horizon glow. I guess a distance shader would help here.

The more I play with TG, the more I realise that atmosphere defines the 'look' of a scene. eg brightness of shadows, scaling objects into distance, smog, damp atmosphere, etc.

[PabloMack]

Haze exp height = gradient control

Okay.  The "exp" was misleading.  So this is the gradient control that I said was missing. 

The haze/blue sky colors = not gray levels only, you can make it any color you like

I see.  You have to click on the swatch to change the color.  I didn't realize that until just now. 

More on-topic. I'd go either for a low level cumulus with a lot of coverage or set the haze density >4 and set exponential height quite low (<1000m for starters). Depending on your camera-height you should be able to see a kind of mist.

This is good information.  Thanks to all of you. 

[Seth]

The more I play with TG, the more I realise that atmosphere defines the 'look' of a scene. eg brightness of shadows, scaling objects into distance, smog, damp atmosphere, etc.

totally agree with that ^^