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Velocity Pass is empty

Hello all,

I am trying to figure out why there is no data being rendered to the Velocity Pass. It just looks empty, with the 0.5R, 0.5G colour.
I have a moving camera and a moving alembic cache, the rest is static geo.
Do you know why nothing is being rendered to the velocity cache?
When I output an image sequence with the MovieRenderQueue, this layer in the EXR is therefore empty.

Thank you in advance for your help,

Only movable objects that moved write to velocity pass.

Thank you for your answer Deathrey,
The alembic was set to movable, so that wasn’t the problem. The real problem was that I was checking the contents of the Velocity pass using Photoshop (modifying the exposure, contrast etc. to show possible values, like I usually do with WS Depth Pass), but I gues it turns out the velocities were so small that to my eye they were not noticieable… When I chucked it into Nuke it did show up…

What a stupid error… hehehe