Volume Velocity in Solaris

[frame48]

I am having trouble getting motion blur to work on a cached VDB simmed with Axiom Solver in Solaris. I have tried using "vel" in the velocity field parameter on the VolumeGrid Shader and also tried using a vdb vector split with "vel*" but nothing seems to work even when bumping the velocity multiplier by 10000. Using a Camera node with Vray physical cam settings, motion blur turned on, etc.

Using build:
V-Ray for Houdini number:22761 hash:954828e from 22 Sep 2024 00:29
V-Ray Core 6.20.23 [e22648ee] from 12 Sep 2024

Is there a trick I'm missing to get it to work? I recall the vdb split method is what usually used to fix this issue Gosho.Genchev or bdancer

[Morbid Angel]

We cannot get velocity to work even with regular vray in houdini, I guess to be determined what the issue might be?

[frame48]

Morbid Angel Just confirmed that it doesn't work at obj level as well. This was working with earlier builds for you too?

[Morbid Angel]

No it never worked, but we are using vray for houdini for less then a year so perhaps it worked at some point.

[Gosho.Genchev]

Hey folks,

I can see from the screenshot that the Velocity is undersampled (the voxel size is different for the velocity field compared to e.g. density and temperature).
This is a trick usually utilized to (1) reduce the cache size and (2) smooth out the velocity vectors a bit, getting rid of artifacts caused by e.g. distrurbance applied right at the boundary of the density (at very low density values).

Unfortunately, this undersampled velocity approach is not supported by V-Ray, and never has been. We're currently working on re-implementing our volumetric shader to bring it up to date with modern tricks and workflows but for the time being, my only suggestion would be to ensure the voxels sizes are the same for all fields.



Best regards!

[frame48]

Thank you Gosho.Genchev! This is really helpful info to be aware of. Maybe adding into the docu would be nice? (Although theres a big chance I missed this)

Best,
Enrique