Displacement Artifacts

[gramx]

Hi

I am exporting 32bit exr ocean displacement maps from Houdini and rendering vector displacement in 3dsmax with V-Ray. I am running into problems with the Max suddivs and edge length as I am having to set them really high otherwise I get small black areas in the reflection map but the diffuse renders fine. This would be ok but its causing very long unnecessary render times! I have checked the cusp of the ocean displacement map to make sure it isn't overlapping any geometry. I am using edge length of 2 pixels and 64 subdivisions, this almost fixes the issue. The displacement plane is also subdivided quite heavy.



Is this a bug??? Does anyone know of any fixes?

Thanks

Graham

[svetlozar.draganov]

Can you send us this scene along with displacement-map for investigation?
Which V-Ray version is that?

[ben_hamburg]

Not sure, but from what I can see on the image those black areas simply are reflections of the black environment...

[gramx]

Great!

Here is link to sample scene:- https://dl.dropboxusercontent.com/u/...splacement.zip

Thanks
Graham
https://vimeo.com/user3624838

[gramx]

Not sure, but from what I can see on the image those black areas simply are reflections of the black environment...

I thought that at first but the environment is full spherical dome with no black in it.

[gramx]

I am using V-Ray 3.00.02

Thanks for help.

[svetlozar.draganov]

The issue comes from DomeLight actually - for some reason the reflections from it are not calculated properly.
If you disable Affect Reflections from DomeLight options everything works fine - you could place the same environment map into reflection-environment-override slot and use that as a workaround until we find a way to fix this bug.

[gramx]

The issue comes from DomeLight actually - for some reason the reflections from it are not calculated properly.
If you disable Affect Reflections from DomeLight options everything works fine - you could place the same environment map into reflection-environment-override slot and use that as a workaround until we find a way to fix this bug.

Thanks for looking into this issue. I have tried switching off the DomeLight and using the reflection-override slot but you still get artefacts in the render this time they are a light blue colour, harder to spot. Again if you increase max subdivisions up to 64 it gets rid of the artefacts.

[svetlozar.draganov]

You are right - at first I was thinking that white-blue color is fine but it is not.
I have added this case into our bug-tracking system for further investigation.
We will let you know when we have some news about it.

[gramx]

Thanks for looking into it, hope it can be fixed soon.
Graham

[vlado]

Is this a bug??? Does anyone know of any fixes?

It's not exactly a bug - these are places where the displacement is too big and causes the surface to flip over - this is plainly obvious if you add a VRayNormals render element. Try using Phong BRDF and it will work better, but in general it would be best to use a correct displacement map. There's nothing else that we can do to fix it on our end.

Best regards,
Vlado

[gramx]

It's not exactly a bug - these are places where the displacement is too big and causes the surface to flip over - this is plainly obvious if you add a VRayNormals render element. Try using Phong BRDF and it will work better, but in general it would be best to use a correct displacement map. There's nothing else that we can do to fix it on our end.

Best regards,
Vlado

Hi Vlado
We have tested this displacement map in both Mantra and Arnold and it renders fine without any flipping or overlapping issues. I'm not sure why the displacement would be wrong in vray, I will try some more tests and check the Normals.
Thanks
Graham

[gramx]

Hi

I have been doing some more tests with vector displacements but still run into the same issue. I have also tried Phong which produced light blue artefact's instead of black.

You can see that the displacement map is working in mantra and Arnold so I don't think its a problem with the map. I did have to flip the axis of the grid to match Y up but I don't think this would cause any issues. Are you sure its not a bug? I don't know what else we can try.

[vlado]

It's not a bug, however I think your set up is slightly wrong. Can you post your Maya scene so that I can compare? If you want to use Object space displacement, keep in mind that the up axis in Maya and 3ds Max is different; there might also be other things that need adjustment. Have you also tried rendering with V-Ray in Maya?

Best regards,
Vlado

[gramx]

Here is a link to our Maya setup, its currently using Arnold but has camera and plane in it that matches the max scene, its also using same displacement map.
https://dl.dropboxusercontent.com/u/...testDispMaP.ma
We have a beta of V-Ray 3 for Maya but we had trouble hooking up the vector displacement map, it didn't do anything.
Thanks
Graham