Question re. matte object

[TERRA Operative]

I have a model I'm trying to render out with a matte object, but I'm having a bit of a problem.

As you can see in the attached image, there is a portion of the model that extends below the ground level.
I have placed a box (the light green box) around this and applied a VrayMtlWrapper material, so it will prevent the model that extends below ground level from being seen with low camera angles.

Problem is, the box just renders black. I just want it to be invisible on the image and alpha, and to make anything it covers invisible too. I don't want it to cast or receive shadows or anything, just act like it's not there at all.

Anyone got any suggestions?

[bob-cat]

Set your alpha to -1!

[TERRA Operative]

Hmmm, that works for the image, but the box still affects the alpha...

Is there a way to stop it from affecting the alpha too??

[bob-cat]

In the material wrapper OR the vray properties of the object, (remember the material wrapper overrides the vray properties) do either:

1. Set your Alpha contribution to "0" -the object will not appear in the alpha channel.

2. Set your Alpha contribution to "-1" - the object will not appear in the alpha channel AND anything behind it will also appear invisible (cut a way).

[TERRA Operative]

Sweet. I'll give that a try.

Thanks.


It seems I was jumping the gun a bit. With -1, When the irradiance map/light cache is being rendered the alpha is affected by the box, but when the final pass is calculated, the alpha is correct. I gotta play with this matte stuff to get my head around it.