Geometry hidden to camera renders odd

[tricky]

We are often in a situation where we want to have some of our geometry hidden from view, yet still affect lighting/geometry. The way we do this is to go to the standard properties of the geometry and tell it not to be visible to the camera.

This seems to work unless elements of different objects are coplanar - for example, a mastic seal against the edge of a bit of curtain walling. In this situation, the coplanar faces render as speckly areas in the image.

Any tips on this?

[trick]

Have you tried raising the transparency levels ?

[vlado]

You can try to increase the secondary rays bias option a little bit and see if it helps, but in general coplanar faces are a problem, even when invisible (V-Ray just makes them fully transparent).

Best regards,
Vlado

[tricky]

So what would be the best way of having objects there from a GI/reflection/shadow point of view and yet not actually visible to the camera? We quite often need to do this kind of thing.

[unknown]

i have had the same problem, it was with hiding a car, both vray matte and just hiden from camera produced loads of black polys showing though.##would be good to know a work around, as using the ray bias messed with the rays in the scene too, especially as I had to crank it up massively to remove the offending polys.

[tricky]

Its good to hear I am not the only one! Another situation is where we want to hide a ceiling but the tops of walls that 'touch' the hidden ceiling render as dirty speckled areas.

[dbibb]

Just had this problem today. It's happening on trees we made in onyx. Cranking the secondary ray bias up a lot (to 0.5) does remove most of the errors. It's not a big deal in this scene, because I'll be compositing the trees back on top.

[Morne]

what happens if instead of in standard object properties you untick "visible to camera", instead of this just set in same window visibility = "0"
have you tried that?

Kind Regards,
Morne

[dbibb]

Thanks for the idea Morne.
Unfortunately, the black errors remain. Also, the trees don't show up in reflections, which is the whole point of leaving the geometry there in the first place.

On a side note, the black specks are part of the alpha channel.