Problem with the "Panning" (motion blur with animated camera) effect / camera motion blur effect

[GabrielChahoud]

Hi guys,
this is my first post here, tks for having me.

Lately, I've been doing some tests about simulating the "Panning" effect with V-Ray 4.20.02 for SketchUp.
As long as SketchUp doesn't have support to objects animation, in order to do any effect related to that work, we need to import the object as an animated proxy, so I animated a car and exported it as an animated proxy to use with V-Ray for SketchUp. Mostly the effect works well, as you can see in the images below (the car is focused and the rest has the "motion blur" effect).



But the problem happens with the wheels. In order for the wheels can work fine, I needed to reduce the number of turns. But if I try to use the correct numbers or If I use the same as I did (290° of a turn) but try to reduce the shutter speed
to make the blur stronger, a strange bug occurs (image below), as if I had a scale animation applied to the wheels as well.


Does anyone know what could've going on?
Tks

[konstantin_chaos]

Hi GabrielChahoud,

I was surprised to see that in the SketchUp forum
What you've described is actually the expected behavior.
The thing is that when V-Ray exports the geometry as a Proxy it stores the motion data as a single velocity direction.
This means that the curved motion will not be accurately stored and eventually rendered.

Use the following workaround if possible:
- Export the animated object as animated alembic files (.abc)
- Load the .abc file as a Proxy Mesh (the same way you've been doing it for the vrmesh)
- Use the following script to change a V-Ray option not currently visible in the UI:

VRay::LiveScene.active["/SettingsMotionBlur"][:geom_samples] = 12

*Note that in the ideal case the geometry samples for only the animated object should be increased.
The script increases the global scene geometry samples - this is sub-optimal.

Let me know if that worked.
We'll consider improving this workflow in the future.

Regards,
Konstantin

[GabrielChahoud]

Thank you very much, Konstantin_chaos! Just knowing why that is happening is very good already, I was running out of hypotheses in my head rsrs' I'll try your suggestion and, once I did it I'll leave a feedback here to let you know if it worked.

Besides that, it would be lovely if V-Ray could support the Fredo Animator extension. That way, we'll be able to do all the work into SketchUp