Terrain clipping as a function of the AA in the renderer?

Started by SteveR, May 03, 2014, 02:07:37 pm

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SteveR

Hi all, I wonder if I could ask for some help.

I am rendering a scene that is going to be a backdrop for a project and the camera position is high up and it is very cloud heavy (although I will attempt to reduce the density of the clouds at some point I think). As such I have been experimenting with the AA to get the best looking result and I noticed that the AA setting is causing the terrain to render clipped.

I attach 2 images, one with AAx15 and one with AAx3 - they both clip the terrain but differently. I actually don't want any clipping at all - any ideas anyone what is going on / what I am doing wrong? I've also included the scene file.

Many thanks
Steve



fleetwood



When you have extreme displacements they can extend beyond the size of a render bucket making them clip.
You may be able to fix that by changing the displacement tolerance setting in the Planet01 node to a value of  2 or 3 instead of the default of 1.

SteveR

Hi fleetwood,

Ah, thank you for this - yep that seems to have fixed it :)

Many thanks
Steve

Dune

You have to take care, though, with increasing it; it causes render time to increase as well. I wonder what would happen if you increase bucket size.... though it wouldn't be the final solution.

Oshyan

Yes, just to be clear about the specific thing that's happening here: Large displacements that cross render bucket boundaries can be clipped with default settings. Increasing AA makes bucket sizes smaller due to more memory used per pixel (I believe), and thus the clipping behavior changes. Setting manually, larger bucket sizes may help as well, without increasing render time as Ulco mentions, but the Displacement Tolerance setting is indeed for this exact problem.

Incidentally, AA15 is a really high value for what your scene looks like. Higher AA values are really only necessary when objects (especially trees and other vegetation) are visible. For terrain and clouds only, AA values above 4 are seldom necessary.

- Oshyan

SteveR

Thanks for the additional info Dune and Oshyan, that's really helpful. I was experimenting with the really high AA as the clouds near camera were looking quite granular, not cracked that one yet. Think it may be to do (in part at least) with the volumetric lighting, so I will investigate into that a bit more.

Oshyan

Grain in clouds is going to come down to the sampling of the clouds themselves, controlled generally speaking by the Quality slider in the cloud layer. Since your scene consists of mostly clouds you might consider trying Defer Atmo/Cloud. You'd want to use low AA values, maybe 4, and a Cloud Quality of 1 to start. But if it doesn't immediately give you any benefits in terms of either quality or render time, then go back to regular (non deferred) atmo/cloud rendering as it can be tricky to fine-tune and get the best results out of the Defer method.

- Oshyan

SteveR

Thanks Oshyan, I'll experiment. Just been reading up in the wiki re defer mode.