Ground Reflection Issue

[brickyard]

Hello,
I have rendered a glass bottle in a black environment, and I now want to render a separate ground reflection as a standalone element with alpha. When I render this with the bottle's primary visibility set off, my reflection not only includes the bottle (as desired) but includes the dome light and my rect lights in the scene. I do not want them included. If I turn off affect reflections on those lights, they aren't there, but the reflection of my bottle looks wrong because the bottle is not getting the proper reflections either. In renderman, I accomplish this by either setting my ground object to only reflect objects and not lights, or by creating a reflection set with a maya selection set and plugging that in to the shader for what it will reflect. I see nothing like this in VRay, is there something I am missing? Thanks!

[Svetlozar Draganov]

Unfortunately Vray currently doesn't have option to disable Light Reflection on a particular object and the only way to simulate this effect is with 2 copies of the same light.
One of the lights should have Affect Reflections ON , and the other one OFF.
Then with relationship editor set the first light to affect all objects except the ground , and for the second light to affect only the ground plane.
Light_Link.zip

[Morbid Angel]

You can create a reflection id matte, which can have the bottle as pure red in the reflections this will allow you to key that object out. But as Svetlozar said its not possible to create per object reflection linking. Though with that said, there is a reflection distance falloff in the shader which can limit the reflection distance of rays for a given object so you can use that to omit the reflection of the dome light but keep the bottle reflected in the floor.

The thing about the physical lighting though is that in real world you couldn't specify this kind of operation, you can't hide the sky (dome) from reflections unless you put them in the room, but then you can see the room in the reflection, vray is geared towards that logic...so if you try to keep the approach as physically accurate as possible you will get good results and it will play nice with vray

[brickyard]

Dmitry,
While the idea of keeping things as physically accurate as possible is cool, the real world isn't composited either. I always need to be able to spit out separate ground shadows, ground occlusion, and ground reflection passes at a bare minimum.

Svetlozar,
Can a feature request be put in to allow for reflection sets (this notion is useful for more than just reflections of course, eg: SSS) which are passed as a maya node path to a selection-set in the scene. This would be an optional string attribute field that the user could simply place the selection set name (shortest possible non-colliding scene path), and only those objects would be counted in the reflection calculation? I can see not wanting to implement type-based exclusions for lights, environments, and objects as a whole due to the physically accurate idea, but being able to create semi-exclusive reflection passes tends to be a pretty big deal and very useful. Thank you!

[vlado]

You can use link linking to limit the reflections of lights only to the bottle. It may not be quite what you need though, if you want the lights to illuminate the ground too.

Other than that reflection exclusions are planned and will be implemented.

Best regards,
Vlado

[brickyard]

Fantastic, thanks Vlado!

[Morbid Angel]

Btw I just remembered. You can use vray reflective occlusion as a render pass, like vray extra texture. In that reflective occlusion you can color the reflected (occluded objects) so you can return pure colors and use them as masks for your ground reflection.