Subdivision surface rendering

[scooternva]

I've gotten into subdivision surface modeling recently and am impressed with OctaneRender's Cattmull-Clark SDS support. I am confused by something though... these are stats from rendering my 9,857 polygon base model in Layout with the OctaneRender object tag settings shown below (all tests using Catmull-Clark SDS, edge-and-corner boundary interpolation, SDS sharpness 0.0, and a single-layer model that is 100% SDS):

• Subdivision Level 1: 80,712 polys; peak memory 5.195 GB; 192 secs
• Subdivision Level 2: 322,842 polys; peak memory 5.297 GB; 200 secs
• Subdivision Level 3: 1.3 million polys; peak memory 5.540 GB; 207 secs
• Subdivision Level 4: 5.2 million polys; peak memory 6.646 GB; 221 secs
• Subdivision Level 5: 20.7 million polys; peak memory 30.2 GB; 240 secs

Peak memory rising with each SDS level, yup that's expected; you're keeping track of more polys at each level. The scene frames take longer to load as SDS level increases, and that's also expected; you're doing more and more computations to generate the SDS polys prior to rendering. But how is it that SDS level 5 (with 256 times the polys of SDS level 1) only takes 25% longer to actually render?

Honestly, even when the camera is right next to my model I can't spot any smoothing issues above level 3, and barely above level 2. If there really is such a low memory and time penalty for higher SDS levels (at least below level 4), why wouldn't I just leave the SDS at level 3? I'm just curious how it's possible that the renderer barely slows down between the intermediate SDS levels.

[LightwaveGuru]

Hi,

It is not the rendering that slows down, but the preparation of the objects and loading into the VRAM. Therefore. The fastest possible rendering can be achieved by freezing all objects into their corresponding sub patch level (no matter if sub division surface or catmull clark). This saves for each frame this process that otherwise octane must perform. so. find the right level beforehand and then render with the frozen models.

snip LWGuru

[scooternva]

Huh... I thought part of the whole reason for using SDS was that you didn't freeze your model, but instead selected the subdivision level you needed. Is dynamic SDS only really used for previz and while you're surfacing your models, and everyone freezes their models when they're finished?