Hi guys,

Has anyone tried exporting a motion vector pass from the sidefx included example on motion vectors? It can be found with the getBlurP node help card.

I notice that I needed to multiply the motion vector by 100x in Nuke in order to get motion blur lengths that look close to what it would be like if the image was rendered with motion blur.

In my other test cases I've sometimes had to multiply the motion vector by as much as 1500x before I get similar length motion blur.

I'm curious if this is to be expected? Is there a way to render out motion vectors that have more reasonable values?

I'm not good with the math on this, so if anyone wants to explain the logic and math behind exporting motion vectors, I'll also be really grateful to read up.

Thanks a lot!
Nelson

For rendering motion vector to use in the Nuke for adding Motion Blur ,I usually use Velocity Vector ,Specially for particles !

Also I use a simple VOP SOP to define amount of the Velocity Vector 8)

In the Attached file I exported velocity vector from Houdini and use this pass in the Nuke to adding Motion Blur with “Vector Blur” node :

The “large multiplier” you need is actually your image resolution in X and Y since the motion vectors from houdini are in NDC (0-1) space! So if your are rendering 1920x1080 just put an expression node where you multiply your motionVector.red * width and motionVector.green * height!

cheers
Oliver