Motion Blur -> Geometry popping

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Hi,

using Vray Next (4.3.002) for Maya 2020.2 (Windows) we have an annoying problem with motion blur: Parts of our rocket (mainly one small cover) are popping on some frames as if it has different "speed" as the rest. On other frames other and more parts seems to be ahead of the rest. Looks like the rocket falls apart.

The rocket is grouped two times: The upper group is attached to a motion path and the group below has some translate and rotate animation.

GI is BF+LC.

The camera is a physical camera with motion blur enabled. We also try the camera overrides in the RS with geometry samples up to 8, but that doesn't change anything.

Any tips would be great.

Thanks
Lars

[Mihail.Djurev]

Hi Lars,

Would you be able to send a stripped-down version of the scene that reproduces the problem to support @ chaosgroup.com ?

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Hi Mihail,

thanks for your reply and offer. We just did another test: And it seems that the "double" animation did cause the problems. When we delete the animation on the group below the scene renders fine.

Don't know it the problem is also related to the motion path or if it it just that if you animate a group below an animated group the motion blur calculation gets messed up.

We now try to bake all animation and hope that this fix the problem.

Sorry, can't send you the scene (NDA). If you can't reproduce the problem we can perhaps replace the rocket with an other object and send it through.

Best,
Lars

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Baking does not help, because the hierarchy with the two animated groups still exists.

Does anyone know a way to bake a hierarchy with two animated groups (pivots are on different positions) to one group/locator?

Is this a known problem with MB in V-Ray? Can't believe. If you animate an airplane and also animate the propellers (of course they are grouped below the airplane), that shouldn't be problem, or?

[fixeighted]

Just a thought: does it work if you animate linked dummies rather than the grouped geometry itself?

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Unfortunately not. Thanks.

[fixeighted]

Ah ok, shame.
I have had issues in the past like this and I think I also tried not using groups at all, instead parent/child linking everything (as groups are a bit iffy in seemingly random situations).
Also scaled objects can cause problems when not transform reset, plus mirrored objects when not reset, etc., so quite a few potential causes

I'm hopeful you'll find the culprit!

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Yeah, the grouping seems to be the the bad guy. The rocket is attached to the motion path, but needs additional rotation and translation in certain situation. The twist attributes of the motion path doesn't do the job here.

Think we need to animate the rocket by "hand".

[fixeighted]

That sounds like progress at least

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Yes, indeed. With some Matrix nodes connections were are now at a 90% solution. Bad luck that our script girl is on vacation

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Has anyone an idea how to edit the node graph on the image to get the "real" world position and translation from x_shell + the group below? At the moment the translation and rotation values from the group below x_shell are not transferred. Thanks.

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Update: We have exported the animation as a vrscene and thought that this is the solution, but nada. We still have the popping and the massive deconstructions (see image). I mean there is no motion path and no grouping when exporting to vrscene, or? Will now try the alembic export. Is there any way to keep the shaders assignment intact?

Thanks
Lars

[Mihail.Djurev]

Update: We have exported the animation as a vrscene and thought that this is the solution, but nada. We still have the popping and the massive deconstructions (see image). I mean there is no motion path and no grouping when exporting to vrscene, or? Will now try the alembic export. Is there any way to keep the shaders assignment intact?

Thanks
Lars

Yes, the vrscene is "flat" in terms of transforms, grouping, etc.
However, we still depend on Maya to give us the correct "flat" transform. The problem lies in the Maya->V-Ray connection somewhere, so exporting to vrscene will not be any different than an actual render.
The problem could be a Maya API bug or maybe we are not using the Maya API correctly in this case.

Unfortunately, we did not manage to reproduce the issue on our end, so it would be great if you can send us a scene. It doesn't have to contain the original geometry or assets, cubes will do, as long as the MB issue is still present.

Cheers,
Mihail

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Thanks Mihail. Exporting to Alembic also doesn't help. Horrible.

Okay, will discuss this with my colleague. Where could we upload the scene?

[Zdravko.Keremidchiev]

Feel free to send it over any file-sharing services you are comfortable with, like WeTransfer, iCloud, DropBox, Google cloud, etc. We can also provide you FTP account if you send us an e-mail to support@chaosgroup.com mentioning this thread.