vdb with motionblur reading the wrong frame

[LeoYfver]

When motionblur is on the rop or a velocity node exists in the renderchannel it reads the wrong frame. so on frame 0001 it reads 0002. When turning on velocityblur on the node it becomes correct. Dont think though that this should be the case because velocity on vdbs are always a vector velocity.

Regards Alexis

[Gosho.Genchev]

It's very convoluted to explain - it's a side effect of how we export the cache paths when Motion Blur is enabled. If you set the Load method to Packed Disk Primitive, everything should work as expected. There's a drop-down for the visualization type where you can specify "Full Geometry" for the Viewport preview.
I think it should be possible to apply the same 'fix' for the case where the volumes are not packed - please ping us if rendering them as Packed disk primitives is not an option for you.

All the best!

[LeoYfver]

and it will be loaded efficiently into the vrscene? should work doing it like that. Othewise could there be an exception for vdb files?

Reagrds Alexis

[Gosho.Genchev]

and it will be loaded efficiently into the vrscene?

Yes, we added support for volumes in Packed Disk Primitives so you can instance volumes and offset the loaded frame using the intrinsic attributes on the packed primitive. In no case should the volume be baked if it's loaded as packed...well, unless you unpack it

Othewise could there be an exception for vdb files?

I thought a single frame wouldn't be an issue so we left it for another time. As you've noticed yourself, setting the Geometry Velocity Blur also solves this. There are 3 things that go into motion blur:
1. Object transformations
2. Camera transformations
3. Deformations (in the case of volumes, this is the vel.* fields)

If you enable Geometry Velocity Blur, you'll lose Object transformations - in other words, if the geometry node containing the volume is animated to move, that won't be affecting the motion blur.
If you keep Geometry Velocity Blur disabled, the motion blur effect will consider all 3 of the above but depending on your Offset/Duration settings, you may end up with the previous or the next frame being loaded.

Hope that helps!

[LeoYfver]

thats really good, thanks, think its the way to go for now.

I still dont understand why the second frame would be rendered insted of just sampling the current and the second frame, but as you said its convuluted

Thanks so much for the info really appreciate it!

Regards Alexis

[psanitra]

Gosho.Genchev I`m running into some issue with motion blur volumes too, they look like they are swimming on some frames, probably loading wrong frame number as you mentioned above Here`s my setup:

-Vehicle, that by itself have deformation motion blur, but is also linked to nulls for global transform(general direction of motion)
-There is volume on the vehicle, snow cover. That is just density VDB sequence cached to disk, with no velocity grid. This volume is inside it`s own GEO node and is linked to the same nulls as vehicle.
- There is motion blur on camera too.

When i render this setup i get some swimming. So what is the "proper configuration" to render the volume?
From what you wrote above, it does not have correct solution? If i enable geo vel blur, i loose obj tranform. If i disable it, i get wrong frame, which is probably what i`m getting now.

[Gosho.Genchev]

on some frames, probably loading wrong frame number

Hmm, if it only happens for certain frames, it might be something else. What Alexis above has hit will be consistent for the entire duration.
Could you try setting the Load method to Packed Disk Primitive to see if that changes anything ?

I'll try to reproduce this here in the meantime.

All the best!