Environment and Fog questions

[corestudio]

I'm trying to wrap my head around vray environment fog. I've read the docs, but while they explain all the parameters they don't really discuss the most basic stuff like how to hook up the nodes.

Environment Fog. I finally figured out that I should check "Use environment volume" in the render settings and hook up a VRay Environment Fog.

1. If I set for distance to 10, shouldn't that mean that an object 10 units from the camera is completely obscured by fog? It doesn't seem to work that way, so I'm looking for a little help in understanding the logic.

2. The other Fog nodes. How to attach these to geometric objects? And can you hook up Vray Environment Fog to geometry?

Note to chaos group: It would be great to have simple scenes for these nodes so we can dissect. Thanks!

[vlado]

I finally figured out that I should check "Use environment volume" in the render settings and hook up a VRay Environment Fog.

Thanks, we should really add this to the help index

1. If I set for distance to 10, shouldn't that mean that an object 10 units from the camera is completely obscured by fog? It doesn't seem to work that way, so I'm looking for a little help in understanding the logic.

The fog is exponential; it never reaches 100% opacity. The physical explanation for the fog distance is the distance at which half of the light going through the volume is absorbed.

2. The other Fog nodes. How to attach these to geometric objects?

You can put them as a volume shader in the material of the respective objects.

And can you hook up Vray Environment Fog to geometry?

Yes, and there are two ways for this. One is to put it as a volume shader for the material of the geometry. A limitation here is that it won't work if the camera is inside one of the objects (unless you surround the camera with an "air bubble" with the same material) or if objects intersect. However, it will work for any objects (meshes, displacement, subdivision surfaces, proxies etc). The other way is to attach meshes to the environment fog node through the Relationship editor - the VRayEnvironmentFog node is also a Maya "set" so you can assign objects to it. In that mode, objects can intersect and there no problems if the camera is inside one of them. A drawback here is that only polygon meshes can be used in this way.

Best regards,
Vlado

[corestudio]

Awesome, thanks Vlado. I could have sworn I tried the fog nodes as volume shaders and it didn't work, hence the question. I'll give it another go. Regarding the "air bubble", do you mean something such as making a sphere (or whatever) a child of the camera using the same material as is attached to the fog object? and it will sort of negate/boolean the fog when the camera+bubble combo is inside the volume of the fog object? Interesting...

I'll also try the Relationship editor.

Thanks much,
Gary

[vlado]

Regarding the "air bubble", do you mean something such as making a sphere (or whatever) a child of the camera using the same material as is attached to the fog object? and it will sort of negate/boolean the fog when the camera+bubble combo is inside the volume of the fog object?

With inverted normals, yes. This came up in a discussion on rendering underwater effects here: http://www.chaosgroup.com/forums/vbu...048#post557048

Best regards,
Vlado

[corestudio]

You can put them as a volume shader in the material of the respective objects.

Best regards,
Vlado

A quick follow up to this. Do you mean, for instance, to drop a VRaySimpleFog into the Volume material of the Shading Group? I can't seem to get this to work. Any chance you have a simple scene around where I can see the connections?

thanks

-gary

[Zdravko]

Here is a very simple example scene.