URGENT: Artifacts on thin objects that are close to each other

[Alex_M]

RT CUDA produces artifacts on the surfaces of objects that are too close to each other. If I space them out a bit the artifacts go away. I checked and the objects are not overlapping. There's a space between them even though small.

It happens both with the official 3.50.04 version and the nightly from my signature. I think it comes from the camera and more specifically the focal length parameter. If I set the focal length to around or over 80 I can see the artifacts and if I set it to around 30-40 they go away. However I can't really lower the focal length since there's a specific requirement for the shots to have less perspective. I tried adding thickness to the objects but that didn't work.

Please let me know if there's a fix or a workaround for this. Any help is appreciated. It's a bit urgent since there are hundreds of 10k shots to be rendered very shortly. I bought 1080 ti mainly for the purpose of utilizing the fast GPU rendering on this particular job but if there isn't a workaround or a fix I'll have to use our CPUs which are 2-3 times slower than the GPUs we have at our disposal.

I can send the scene for a test if necessary, let me know. And here's a screenshot that illustrates the problem. In the bottom one you can see that there are no artifacts when the object is spaced out more:

[matanov]

Try playing with the Secondary rays bias in Global switches.

[Alex_M]

Hm.. Doesn't seem to do anything. It was originally 0.0. I tried 0.001, 0.01 and 0.05 but it looked the same. Is there any specific value that would work?

[goyko]

Hi, you can send a simplified scene that reproduces the problem to deyan.ivanov@chaosgroup.com
Before that, if this is in MAX, try making your scene smaller, if it is possible. For example: if the B3 plate is 100 generic units wide, scale it to 1.

[Alex_M]

Hi Deyan,

The scene is in real world units (cm) and most of the power distribution units are 150 x 5 x 5 cm on average. I think this shouldn't be an issue? I just emailed you a scene for tests and troubleshooting.

[goyko]

After some investigation, I consider the geometries to overlap in a weird way. I think it would be fastest if you remodel the engraved plates to be more planar, if possible. VRay Adv handles intersections with double precision floats, which obviously solves this, but is not possible in RTGPU at the moment.

[Alex_M]

Thanks for your email, Deyan. I really appreciate looking into this. So it seems that the CAD model has some very tiny irregularities of some sort which causes Z-fighting and because of GPU not being capable of double precision floats these artifacts appear. Unfortunately it will be nearly impossible to remodel the problematic objects due to time constraints so I just ran the renderings on Adv and so far so good! I will have this in mind for the future, especially with imported CAD data. Thanks again for your help!

[Morbid Angel]

Thanks for your email, Deyan. I really appreciate looking into this. So it seems that the CAD model has some very tiny irregularities of some sort which causes Z-fighting and because of GPU not being capable of double precision floats these artifacts appear. Unfortunately it will be nearly impossible to remodel the problematic objects due to time constraints so I just ran the renderings on Adv and so far so good! I will have this in mind for the future, especially with imported CAD data. Thanks again for your help!

Just curious why its difficult to remodel that piece, or do you have multiple pieces like that? it seems quite a simple shape.

[Alex_M]

Just curious why its difficult to remodel that piece, or do you have multiple pieces like that? it seems quite a simple shape.

From what I observed in my own tests it's not the labels that are the problem but the housings which have intricate industrial design. The labels were remodeled in Max as splines with no thickness and then used across all models. Once I put a box under the labels instead of the original CAD housing I don't see the artifacts. So since there are hundreds of models it's not feasible to remodel the housings because of the time constraints.

[Morbid Angel]

From what I observed in my own tests it's not the labels that are the problem but the housings which have intricate industrial design. The labels were remodeled in Max as splines with no thickness and then used across all models. Once I put a box under the labels instead of the original CAD housing I don't see the artifacts. So since there are hundreds of models it's not feasible to remodel the housings because of the time constraints.

what if you put a pro optimizer on it at 100% would that make a difference?

[goyko]

Quick note: after heavy investigation we have a fix for this precision issue in RT GPU. It will be available in the internal beta nightly from 01 June 2017. It will most likely be available in the upcoming V-Ray 3.6 release.
Please try the fix if possible, hope it helps.

[Alex_M]

Nice, I will try it out and let you know about the results.

[matanov]

Have you tried it? It's in the latest nightly.

[Alex_M]

OMG, yes!!! No surface artifacts anymore! Thank you for fixing this.