Tri-Planar materials "moving" when re-rendered.

[seandunderdale]

Hi,

Im finding that my leather shaders are "moving" so to speak when I re-render my shot. I have tri-planar, with random offset and rotation set (perhaps here is my problem). One render, the leather grain is in one position, if I re-render the leather grain updates and changes. The scale is the same, but its like the map has moved. Is this caused by the random rotation and offset? Does it randomise it every time its rendered?

[piotrus3333]

depends on the “randomize by”.
but I do not know how it works in vrscans.

[seandunderdale]

There isnt a control for it in the shader, which is why I was wondering if its auto randomising it when the box is ticked. The purpose of it is to allow you to have same same scan applied to different surfaces and make them not look identical, which is great. However, do you need to untick the randomise options once you are happy with the way it looks? Fortunately the client hasnt called me out on it yet, but I can imagine some would...and I dont think there is a way to revert back to an old randomisation position....there isnt a seed number for example.

[piotrus3333]

might be different than regular triplanar node. there is whole list of properties you can base randomisation on. obj id, mat id, node name etc.

[Ivaylo Katev]

The randomization is just to prevent equal appearance of multiple node instances, it must NOT change the result between two renders. In general, there rendering determinism is basic requirement, even with different thread number,DR rendering etc, if the render is not deterministic this is a bug.

[Ivaylo Katev]

Can you specify the system details? We have sheduled similar issue under Maya, perhaps it appears not only in Maya

[seandunderdale]

Im on Maya 2020 and V-Ray 5 for Maya, update 1

(v5.10.20, revision 30800 from May 26 2021).

Windows 10, rendering local on one pc.

A seed number for the random offset and rotation, as mentioned before would be great. That way Id have more control over the look, and could also revert to previous ones if needed.

[Ivaylo Katev]

Yes, sounds like the same issue, it happens only with Maya 2020 , you observation that it's related to the randomization is helpful

[seandunderdale]

This is still happening in Maya 2022

[seandunderdale]

Any news on whether this can be reproduced in 2022 at Chaos Group end? Kind of makes using VR scans a gamble for car interiors if the textures jump around with every render. Fortunately the problem doesn't happen with animations.

[Ivaylo Katev]

Unfortunately the problem is hard to reproduce and investigate, perhaps you can help us with some observations.
For example: "Fortunately the problem doesn't happen with animations." is this for sure? It can be important information. Another question - is it sure that the problem appears only when the offset/rotation randomization is enabled? Can you provide two PNG images with different result caused by the problem?
And one more - can you export the scene into vrscene format and try to render it with the stand alone VRay?

[seandunderdale]

When I say it doesnt happen with animations, perhaps that was unclear. What I mean is, it doesnt happen between animated frames. Textures arent popping and moving from frame to frame. Once I get my current project wrapped Ill do a few tests. I will also test the random offset / rotation too as I am not sure at all its related.

[Ivaylo Katev]

What I mean is, it doesnt happen between animated frames. Textures arent popping and moving from frame to frame.

This is perhaps an important info, thanks

[Ivaylo Katev]

Some updates.
I was able to reproduce the issue, apparently the origin is in Maya itself. For some reason each Maya session exports the meshes slightly different (only for 2020+ versions), the differences are really really small (in the 6th sign), and in normal situation are totally invisible. However, in VRay and in the scanned materials particularly we average multiple raypaths to obtain the final result,and apparently in the vrscans shader small change in the geometry can lead to totally differen choice of ray paths to average. These paths are still correct, i.e. if you average big count (high image sampler settings) the issue disappears. But when the image sampler settings are low, there is clearly visible difference between each render with new Maya session. We can't fix the Maya meshes , however we will try to remove the big changes in the raypath selection caused by small changes in the geometry.

[seandunderdale]

that is great news. I have been rendering shots with what I would consider to be production settings to get noise free images, so Id be very interested to know what settings are needed to remove the issue. My go to settings are usually 1/60 (give or take 10 on the max side) and default 0.010 for noise threshold.