Black horizon line and artifacts

[markus_s_cg]

Hi,

Why do I get a black line along the horizonline (background i vray sky), and also black spots/artifacts in the ocean surface in the distance?
I have tested with the latest nightly phoenixFD_adv_31201_max2019_vray4_x64 and before that I had 31200 (both has the same issue). I saw something about black artefacts near the horizon in the changelog, but this must be something else?

[georgi.zhekov]

Hello,

If you're using an ocean preset - it creates a V-Ray Plane underneath the simulator so you can get proper shading of the foam and splashes. In the case where the horizon is visible you can just remove the V-Ray Plane and create a huge plane below the simulator and assign a black material to it so you can get the shading of the particle correct without the horizon issues.

Another thing you can do is to set the Reflection glossiness of the Water material to 1 and increase your Ocean subdivs - note that you should be really careful when increasing the Ocean subdivs as you can really easy run out of RAM. You can find more about it here - https://docs.chaosgroup.com/display/...endering-Ocean

Cheers,

[markus_s_cg]

I didn't use a preset, so there was no vrayplane in my scene before. It doesn't seem to make a difference if I create a vrayplane either, or if I try the preset.

[georgi.zhekov]

What if you change the material or increase the subdivs as I mentioned in my previous post?

[markus_s_cg]

Increasing the glossiness to 1 helps a lot but doesn't remove it entirely, but i get some 1 pixel fireflies in the water when I have it at 1.0 Thats why I had glossiness at 0.97 before. I could send the scene file....

[georgi.zhekov]

A scene file would be helpful. You can attach it here or send it to support@chaosgroup.com with a link to this thread.

[markus_s_cg]

Thanks. I sent a scene file to support (email). I might render it with an HDRI sky instead but I had the same problem then. Adding some fog/haze or coastline to cover the horizon would probably help, but was hoping for quick solution.

[Paul Oblomov]

Try to switch to blinn.

[Ivaylo Katev]

It seems to me that the dark line is caused by reflection rays that are directed under the water. In general your image shows a well known problem, that is very probably related to this behavior - apparently the normals near to the horizon are tending to be directed upward, instead toward the observer. The real ocean horizon surface normals are directed *toward* the observer , because the rays always hit the surface near to the highest elevation, i.e. the wave crests, and this happens in a point that is inclined toward the observer. This rapidly changes the optical behavior, first the reflection rays are directed upward instead parallel to the surface, and second the refraction rays have bigger weight, that makes the horizon visible (otherwise it would blend with the sky). I'm not familiar with the latest Phoenix versions, and can't say why the normal inclination is lost (perhaps the Horizon Roughness parameter is controlling this effect), but if you cant achieve it playing with the controls, you can try to introduce it by hand by a fall-off map

[markus_s_cg]

Thanks for the technical explanation Ivaylo Katev I started experimenting with putting two different normalmaps in a distance falloff map node. Not sure if this is the way you were thinking, but then I discovered something. I think Paul Oblomov is on to something. I get a similar dark line on the horizon even if I render a simple vray plane with a white glossy material when I use microfacet GTR. The line disappears when using Blinn...?

[thescopeteam]

I have the same issue in Vray 5, simple plane, sun, and sky, still could figure out what causes this. Its not the arial perspective, its not GI, not displacement

[georgi.zhekov]

I have the same issue in Vray 5, simple plane, sun, and sky, still could figure out what causes this. Its not the arial perspective, its not GI, not displacement

Did you try the suggestions from above? Setting the reflection glossiness to 1 or switching to the Blinn mode?

[waaazoo]

if you remove the Vray Plane, the line goes away. But then, I found also that the horizon roughness changes a little it's behavior. That should be resolved, as it might be needed, sometimes, to keep the Vray Plane.

[Svetlin.Nikolov]

Strange, there should be no connection between the underwater plane and the horizon roughness. Can you share a comparison? Maybe it's something else that is causing it.

Cheers!

[waaazoo]

Strange, there should be no connection between the underwater plane and the horizon roughness. Can you share a comparison? Maybe it's something else that is causing it.

Cheers!

I will double check asap. Thanks Svetlin.