Corona volume material

[3dboomerang]

Hi;

I'm setting up an HDRI environment, with the aid of "Mist" coming from the Corona Volume Material. I turned the HDRI 360° and made some renders to check.

Getting some anomalies, does anyone recognize this? Globe of light moving across the "lens" when the sun is behind the camera? How can I prevent this from happening?

Grts

[pokoy]

Interesting... not sure if related, but what's the directionality value in the VolumeMtl? Does it look different if you change it?

[3dboomerang]

Directionality is on -0,99

Did some tests to check the changes:

I need it on -0,99 though, the sky needs to stay clear and the mist should be located on the bottom of the horizon.. hmpf

Any ideas?

[TomG]

Might be better using a Distance map from the ground to control the clarity of the sky by fading out the absorption (and scattering) as the mist gets further from the ground, and then removing that extreme directionality from the volume. If this is 3ds Max, "Inside Volume" mode might be cool too, then you could add some noise to the Distance map (either in to the distance map, or by combining the noise with the result from the distance map).

[maru]

This is expected if you are using directionality. High positive numbers mean that light in the fog will continue on its way from the light source (godrays), and high negative numbers mean that light will be "reflected" back to the light source. So if you have a sun, which is behind the camera, the sunlight will reflect back into the camera.
You can imagine this as reflection and refraction. Imagine fog as tiny particles in the air. With 0 directionality the refraction and reflection of those particles are balanced. If you use positive numbers - there is more refraction than reflection going on. Negative - more reflection than refraction.

[3dboomerang]

So the Corona Sun is causing this "effect" - Is there any way to disable this cause I can't image this is a desired effect, by anyone's usage of the Corona Volume shader?

"Might be better using a Distance map from the ground to control the clarity of the sky by fading out the absorption (and scattering) as the mist gets further from the ground, and then removing that extreme directionality from the volume. If this is 3ds Max, "Inside Volume" mode might be cool too, then you could add some noise to the Distance map (either in to the distance map, or by combining the noise with the result from the distance map)."

Yeah there are alternative ways to get the desired effect, I'll try and find a different path to the same effect I suppose... Annoying though.. I could simply drag this Corona Volume shader into the slot from from a library, but now I'll have to select objects in the scene each time and do this and that...

I already tried with a noise map in those slots but they look to much like 2D-mapping on top of the image. Might need (alot) more tweaking.

I'll post some stuff if I can generate an alternative.

Grts

[TomG]

Well, I would say that at a directionality of -0.99 that is in fact the desired effect - bounce most light back at the light source; and that directionality isn't the way to create a fog effect that stays close to the ground. For noise that avoids the 2D mapped on the surface, using "Inside Volume" mode is the way to go. To avoid using the Distance map, you may be able to do something such as just use a cube, or other actual geometry of the fog shape, to limit the height of the fog rather than a global environment material.

Not sure about what is meant "select different objects each time" - it would just be done once as part of the scene set up, no different than the initial clicks to set up a Corona Sun in the scene for example.

[romullus]

So the Corona Sun is causing this "effect" - Is there any way to disable this cause I can't image this is a desired effect, by anyone's usage of the Corona Volume shader?

Of course it's a desired effect. Without it would be very hard to get godrays. You're simply misusing parameter and then don't like the effect. It's the same if you'd use anisotropy and then complain about stretched reflections :]

[3dboomerang]

Ok ok.

[3dboomerang]

I've been playing with the Corona Volume shader, inside volume mode + from surface, I'm really not getting any decent results. I even copied the settings they gave in the help-test-scene from their dev video but to no avail.

Can someone point me to a help file on this subject so I can have a in depth look at what all these properties do in respect to eachother? "Winging it" is not gonna work here obviously.

Currently going over tutorials on youtube etc but the settings in those videos are from the older versions

[TomG]

The properties work the same in the new version as in the old, the only difference is the new "Inside Mode" which doesn't affect what the other properties do - it simply affects whether the actual volume inside the object is rendered during the calculations (including distributing the noise throughout that volume so that 3ds Max noise maps are truly 3D and not just calculated on the surface). So the information in the YouTube tutorials still applies, as all Absorption, Scattering etc all do the same things they did before (just that any Noise map into those parameters will be calculated in 3D, and the volume rendered).

The "Step" parameter should be well explained in the tooltip, for the other thing that Inside Volume mode does compared to On Surface.

Note that using Inside Mode will take longer to render, and this will be especially true if Single Bounce Only is disabled - hard to tell from your scene if any of the settings are wrong, as it looks like the results would be fine except that the render hasn't run for enough passes to clean up. What does it look like after enough passes have been done to start to clean up that noise?

Thanks!

EDIT - PS not sure what is happening with that circle in the sky and in the top right; if that is part of the problem, we'd likely need to see a copy of the scene to figure out what is happening, as I've never seen a result like that before from volumetrics.