Nasty shadow on displaced material

[rubberchicken]

I've applied a texture displacement to the ground plane, good quality 4K map. I set it to 2K on the displacement node LOD, which seemed enough. However, the shadow under the jar becomes really dark with a sharp termination. I found that setting the map to 4K improved it a lot but only setting to 8K made it equal in smoothness to the plane without the displacement. Needless to say setting the LOD lower makes the shadow wider again, but still with a hard edge. I'm not understanding why that resolution can be affecting the shadow. The light from a regular Modo area light.

[elsksa]

Hi, interesting case. I'm a Standalone user and don't know much about Octane Modo, funk would. However, out of curiosity, by LOD, do you mean mesh-LOD or is it related to a native Modo feature?

What about scene-scale and its correlation with Rey Epsilon?

[rubberchicken]

By LOD I mean level of detail in the Octane Displacement node, it seems to be called that in the schematic but it is where I can select the resolution for the displacement. Yep, I tried lowering the ray epsilon already. Scene scale is real life... the jar is about 75mm diameter. I'm pretty new to using octane. It's a head-scratcher.

[rubberchicken]

Ah. I have been directed to the docs on displacement for another topic and now see that increasing the displacement LOD can reduce cast shadow artifacts. As I did find. I really do not see having to increase to the maximum of 8K to remove the artefacts as being acceptable. That seems a very strange normal. As is not being able to use both a normal map and a displacement map on a single mesh. Very strange.

Quote…
Level Of Detail - Adjusts map detail quality. Higher values reduce artifacts seen in shadows cast on the Displacement surface and brings out finer details, but it increases render time.

https://docs.otoy.com/StandaloneH_STA/S ... cement.htm

[elsksa]

Indeed. I personally refer to it rather as a "texture displacement resolution control" (at displacement node level) since "LOD" is often commonly associated to meshes, even in offline rendering (since it's typical of game-dev workflows too). EXR + the appropriate disp-tex' "LOD" would usually yield an expected result as long as the scene is correctly setup (such as the scale).

[funk]

We've talked about this on skype, but texture displacement is voxel based, so can be really fast, but has several limitations and can produce artifacts.

It's great if the artifacts aren't noticeable, but once you start running into issues, you need to use more traditional vertex displacement (the "vertex displacement" node).

Since you are working at small real world scales (small product shots) you will almost always need to reduce your ray epsilon (try dividing by 10, so "10um", or "0.00001") to avoid shadow artifacts.

Texture displacement doesn't respect the kernel ray epsilon value the same way as geometry though (it uses larger values), so this may not help in this particular case.

[rubberchicken]

I tried vertex displacement and that seems to be fine, once I saw the note about loading the Modo cage.