I'm trying to get velocities blur (and motion vectors AOV) to work in Karma, Houdini 20.0.59, and just cannot.

Attached is a test case hipfile and screenshot.

I tried:

1. Particle system with @v attrib copied to @velocities. Velocity Blur enabled. Cache node after my render settings. No motion blur at all.

2. Animated mountain and transform SOP on sphere. Random huge @velocities attribute (also copied to @v to visualize, see screenshot below). Velocity Blur enabled. I'm getting motion blur, but it's the correct (i.e. deformation) blur, and ignoring my velocities attributes.

Even though I can see the velocities attribute in my scene graph! (and they are the random huge ones).

Why are the velocities being ignored?

P.S. I also want motion vectors AOV, but it keeps appearing black. See attached hip.

In usd you need time samples to make effects like motion blur happen as far as i know.
In 20 i think they improved somehow how to create them, try to search on that

Hi!

You need to enable the Velocity Blur property on your points using the Render Geometry Settings LOP:




Cheers!

1. no need to rename v@v to v@velocities, v@v is usually correctly imported as velocities

2. the reason you are not getting velocity MBlur is that you are using Scene Import, which will author /geo1.primvars:karma:object:vblur based on the Object's settings, in your case 0, so either set
- /obj/geo1 Render/Sampling/Geometry VElocity Blur to Velocity Blur
or
- override /geo1.primvars:karma:object:vblur to 1 or block it using Edit Properties or Geometry Render Settings

since Velocity Blur Settings on Karma Render Settings is used only for objects that don't have this property explicitly set

Thank you!! Yes both methods worked!

P.S. All the documentation I found said that there needed to be a velocities attributes. So seeing that I had no motionblur, out of desperation I tried that.