Avoid artifact on object with layer visibility OFF ?

[fantome]

Hi guys.

I have 3 cylinder overlaped, each object has his own object layer.
when i set on one of those object
- general visibility to 0
- camera visibility OFF
- shadow visibility OFF
I was expecting that the object become totaly invisible in the rendering.

But, i have a black artifact on object on every area where the hidden object overlap with the visible object.
How could i get rid of those artifact in order to get the exact same thing i would get if i disconnect the object from the rendering group.

All object visible :

Hide object with object layer visibility disable ( black artifact ) :

Hide object by disconneting it from the render group ( object perfectly invisible ) :

Thanks for your lights !
Cheers
E

EDIT :
in my exemple i am able to solve the issue by using a very very small ray epsilon, but if someone can explain me what happen in the background , i would happy to understand .

[bepeg4d]

Hi,
what are the dimensions in cm of the cylinders?

ciao Beppe

[fantome]

Hi beppe, Thanks for your answer.

The scale of the object is 8cm x 19cm x 8cm.

overlap_artifact_01.orbx

(158.78 KiB) Downloaded 128 times

I have attach the scene just in case.
It' s an octane 2019 scene by the way.

Cheers
E

[frankmci]

Looks like our old friend, Ray Epsilon, is the culprit. At that scale, you need to drop it down another decimal place. Odd that the geometry of a hidden layer still has influence, but tweaking that setting will eliminate the artifact.

[fantome]

Thanks for your answer frankmci !
Indeed ray epsilon did solve the problems but i agree with you

Odd that the geometry of a hidden layer still has influence.

i don't understand why the object has any sort of influence when all his visibility options are set to OFF.
there is something in the background that i don't understand and that seem illogical.
why an invisible object can have influence in the scene when it is invisible ?

if a technical mind can help me to understand what octane really do in the background it would be nice !

Cheers
E

[Zay]

The reason is because the hidden object intersect with another object - or is too close to it.

You can turn "Ray Epsilon" down as a quick fix, but I will not recommend that as it will create shadow artifacts in your scene.
Another quick fix is to scale your scene way up which might fix it but can create other problems.
Best fix is not to have object intersect with each other. Or move them a little bit away from each other.

You will also have the same problem in a very big way if you use displacement maps. Yes, it is very annoying and maybe in the future Otoy can fix this.

Here is a test scene you can play with.

[Zay]

Oh and the displacement problem I talked about you can see here:
viewtopic.php?p=323011#p323011

[fantome]

Thanks a lot for your answer Zay, the scene is really useful to visualize the size of the ray bias controlled by the ray epsilon.

So at the end when setting all object layer visibility parameter to OFF, it doesn' t mean that the object is ditch from computation ( it's not like disconnecting it from the rendered geo ).
The object exist in the scene and it will influence the render if object are intersecting each other. Problem like this might be more important on small scale scene.

That would be nice to have a toggle parameter in object layer that allow a TRUE ditch from computation.

Cheers
E