Hello! I have a smoke volume and render camera, both travelling in the positive X direction at the same speed.


In this situation, I would expect to see only the background being motion blurred as it moves past the camera.
However, the smoke volume is also being motion blurred.


This is my Solaris / Karma setup (.hip also attached)


I have tried many different setups, but just can't work out how to resolve this.
Note: I'm using Houdini 19.0.531 due to work version restrictions. Is this the problem? Is there a way around this issue?

Your volume is "deforming", so it is expecting a vel volume for velocity blur.

Alternatively, since all you want is transformation blur, if you pack the volume before applying the anim, and set the sop import to import packed primitives as xforms, and move the cache LOP after the merge LOP, you'll get the expected result.

Here's a hipfile that shows it working using both methods.

Hi thanks for this npetit

If I try your first example of packing the volume before animation, then on the sop import set the packed primitives to create xforms, the volume does not render at all.

However your second example of adding the point velocity surface attribute to the volume does work.

I'll translate some of what I've learnt here into my problematic scene file. It's a little more complex than what we have in this simplified example here, but this is helping me get my head around what might be required.

npetit
Your volume is "deforming", so it is expecting a vel volume for velocity blur

I think LOPs could do a better job of translating Volume primitives into USD and treat volume intrinsic transform as Xform property instead of forcing volume to be "deforming"

As I was searching for a solution for my volume/motion blur problem I bumped to this kind old thread which explains exactly what I am going through with H19.5.

I am having the same issue, volumes that are moving at the same speed as the camera are being motion blurred and the holdouts I that am using which are geometry also moving at the same speed too are not so their are not matching.
But in my case I am not SOP importing but reading the volume with baked transformation from disk using a volume lop, is there any solution for that?

Thanks!