Particle Motion Blur

[patryk_pawlak]

I have failed to find a reliable info about how to set particles motion blur with v-ray,
Could you please provide simple example scene?
I use RTX V-Ray and Houdini 19

Thanks in advance
Patryk

[Dubbie99]

Make sure your particles have a @v velocity attribute.
at object level, make sure that you set the sampling to use velocity for motioblur samples.

[patryk_pawlak]

what is the proper velocity calculation method? Backward Central or Forward?
I belive in 3ds max it was Forward but in Houdini it seems to not look properly
Does V-Ray use properties other than "v" to calculate motion blur?
like "vtarget" or "id", "ptnum" "w" ?

[Gosho.Genchev]

Hey patryk_pawlak ,

As Dubbie99 has clarified above, the workflow is the same as Mantra - use a Trail SOP to compute the velocity if there isn't one coming from the particle simulation, and set the sampling to "Velocity Blur" on the Geometry node.

Does V-Ray use properties other than "v" to calculate motion blur? like "vtarget" or "id", "ptnum" "w" ?

No, V-Ray will use the "v" value directly. You can use the "Match by Attribute" option on the Trail SOP (right at the bottom) to give it an "id" attribute so it doesn't rely on the point numbers (which will inevitably give you issues with changing point count).

Acceleration blur is sadly not supported at the moment - we've implemented support for subsampling both for live geometry and alembic caches that can somewhat alleviate the issue, though.

what is the proper velocity calculation method? Backward Central or Forward?

Assuming you're using the standard workflow of Duration:0.5 / Offset:0 - you should set the method to "Central".

Hope that helps!

[ben_martin1]

Hi, I have also found that you might need to put a timeblend on the points to get velocity blur to work. Even if the timeblend is breaking the deformation blur or subframes this seems to fix vray's velocity blur. I find without adding this timeblend and using vel blur the points render as a streak being pulled toward the origin. Hope this helps.