Mtlwrapper, reflection

[nomads]

Hi

I am trying to composite a chrome ball onto a background plate. I have a spherical HDRI as my light source/ reflection.


The ball sits on a ground plane. The ground plane has a mtlwrapper. Set to matt surface alpha contribution -1



How do I get the reflection from the HDRI onto the ball? The ground plane is blocking it.

Any tips

Thanks

N

[nomads]

At the moment I am putting my HDRI reflection map into the diffuse of the base material.

Is that correct?

[Morbid Angel]

there is two ways you can do it. One you can project your plate onto the ground plane. The other you can just exclude the plane from casting reflection.

[nomads]

Thanks Dmitry, I will try that.

What is the best way to set up correct GI with mtlwrapper ground plane.

N

[svetlozar.draganov]

The GI configuration depends more from Scene Type (Still, Animation, Interior, Exterior etc) rather than matte plane.
Can you give us more information about the scene?

[nomads]

It's more of a generic question when using ground plane and Mtlwrapper and GI.

If the plane is invisible to reflections will it produce the correct GI or should it have a texture in the diffuse base.

In this case I am using a baked light cache and Irradiance map.

[Morbid Angel]

You have to think of the ground plane as a self illuminated material. Since the plate is not modified in any way, one would assume that projecting it from camera onto your ground plane geometry via self illuminated material will produce both proper reflections and gi.

However there is a catch, your object must cast shadow first on to the ground, it will be very apparent if it doesn't.

[nomads]

The shadow was going to be my next question.

So what method do I use to set it up correctly?

[Morbid Angel]

It really depends on how far you want to take it. Some one on this forum asked this question and it was discussed already - you can produce a mask using shadow/light map (you should look up that thread).

You can render a shadow pass and project that with your plate (not ideal)

I typically assemble my scenes in the post software like nuke, so this kind of thing where I get some minor bounce and fill from projected plane without shadow is enough.

[nomads]

I have shadow reflected and Gi

I baked the gi using a standard material then swapped materials on the ground plane to the Mtlwrapper.

I think it looks correct? what do you think?