VRay-RT (Cuda) giving strange 'jaggies' whilst ADV doesn't......

[JezUK]

Dear Chaosgroup,

I need an urgent solution to this, and I have posted on the RT forum (https://forums.chaosgroup.com/forum/...when-using-adv) but feel I'll get a quicker reply here.

Basically I have a client project which screamed for me to use RT, Ductwork products set within a studio (my intention is to also use HDR Light Studio) - and I have invested in 4 x 1080ti gpus which cut through renders.

But yet again, I'm finding myself questioning my decisions as it appears that RT rendering is troublesome.

I have spent a fair bit of time isolating the issue below which to be honest, I simply wasn't expecting to be renderer related.

Here is the render of my ductwork, and you can see where there are 'jaggies' - one would immediately think this is related to anti-aliasing......






I then tried with a basic VRayMtl as an Override and those jaggies still appear (very strange !!!) - remember this is using RT (Cuda);




I then question the model (these models were supplied to me) and were created in Inventor)...... - so I try the same render using ADV (so, obviously CPU based) - and the problem disappears........ (see image below);





Finally, I try to see this from a different camera angle, and the problem exists when RT is used (CUDA) yet goes away when rendering in ADV (see images below respectively);







(image below using ADV - no strange results here);




Please can you advise - as I have a lot of products similar to this one and don't feel confident to take the RT road whilst this is an inexplicable issue for me.

I can send you the scene file if required.

Many thanks.

[matanov]

I can send you the scene file if required.

Most of the times it's the quickest way of helping you

[JezUK]

Most of the times it's the quickest way of helping you

Peter,

I'm preparing the scene file to send to you.

Can I send it to your urgent attention please ?

Kindest regards,

[JezUK]

Peter, I've sent you a WeTransfer link. Many thanks.

[matanov]

Seems like an overlapping faces issue. You can workaround it by increasing the secondary ray bias (Global switches). The workaround won't be needed for the next V-Ray release (we changed some stuff that fix this case).

[JezUK]

Hi Peter,

it?s not caused by that.

If you delete all the objects in the background that are not the subject of the render, and only leave the main subject, those marks will disappear in RT gpu.

[matanov]

Often the overlapping issues are affected by objects that are not part of the problematic ones. Have you tried the workaround?

[JezUK]

Thanks Peter,

I tried what you said and Secondary Rays Bias fixed things.