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I've got a huge interior cylinder about 20km long & 4km in diameter with hills, a grassy texture, and a few trees. There's a giant mirror at each end of the cylinder to make it look infinite.

The hills are flashing. I thought I'd ramped up the GI settings, but they're still flashing. What am I missing?

Using Path Tracing. I've tried GI clamp at the default (1000000.0) & at 10 with no noticeable difference. Because it's a big scene I raised the Ray Epsilon from .0001 to .001, although that didn't make any difference either and the scene looks terrific either way. Max Diffuse & Glossy Depth both at 32. Other kernel settings at default.

Any advice appreciated, thanks.

What is the value of the "Coherent Ratio" parameter? ... try to set it to 0% if it has an higher value.

Anyway I am not sure if a scene with this scale could be rendered with artifacts in Octane. Have you tried other kernels?

-Juanjo

Yes, Coherent Ratio is zero. No, I'll try other kernels, thanks.

I'm still getting the flashing with PMC. I guess I should try Direct Lighting.

The manual explains what the kernel controls are for, but unfortunately none of the controls appear to help with GI flashing.

It is a weird issue, probably a scale problem. If you want to send me a sample scene with this problem, I could test it here.

-Juanjo

The problem went away with Direct Lighting Kernel at very high settings but now there's a new scene that is flashing no matter what I try. I would like to send it to you. I've sent you an email message to work out how to go about that.

For clarification Juanjo said this:

Simple Epsilon Math

All figures in meters. The ratio is the smallest polygon versus the full scene size.


Scene ratio: Recommended epsilon value

1/1,000,000: 0.1

0.001/1,000: 0.0001

0.001/1,000,000: Not possible because the difference in size is too great. One can still try to render a scene in two or more passes

“The simple precision math means that your scene geometry can have about six or seven significant decimal digits between the full scene size and the smallest polygon.”

So, the upshot was that my scene was too big with very small polygons in the foreground. Going to render in two passes instead...

One side note: the scene size is not only the size of the bigest objects available in the scene, but also where they are located. If you have a 1 meter object, but located 100 km. far away the scene 0,0,0 origin, the scene size is going to be 100 km, and you can have also problems to render small polygons.

-Juanjo

We’re actually still having problems with this. We were working on some other scenes for a couple of weeks but now we’re working on another one of these scenes that takes place inside a cylinder space ship that’s about 20 km long with highly detailed characters walking & talking.

It’s very annoying and frustrating that we have no choice but to do foreground and background passes for these scenes because doing so uses up a lot of time and money. A great deal of the time we’re able to shoot scenes in a single pass and still get great results without having to resort to After Effects work and the only reason we have to composite these scenes is owing to the Octane scale limitation, which as I understand it, exists only for the sake of users who own cheaper GPUs that can’t do floating point calculations.

We also use up a lot of time and money completely resetting the foreground scenes. It’s not enough to remove most of the giant cylinder’s geometry, everything has to be moved to the origin, or we still get the GI flashing. If there’s a light far from the scene origin, or even just a null far from the scene origin, or an object like the cylinder with the relevant geometry several kilometers from the object’s local origin (but otherwise near the scene origin), there will be GI flashing. It’s a lot of work to sort this out for every scene. One of our characters has a lot of hair which requires two separate dynamics passses. MDD’s can’t be reparented, so the dynamics work can’t be completed until the scene’s been moved back to the origin. There are all sorts of difficulties involved.

There’s only one way to solve this properly. Otoy needs to step up and offer two versions of Octane. One for non-floating point GPUs and one for GPUs which do support floating point operations. The current situation is just too limiting.