Hasta La Motion!

I am trying to get a motionvector pass from a fluid.
i’ve red that if i convert The fluid into polygons i can output a motion vector Pass for the Fluid.
My fluid (the polygonal version) is on a seperate layer. Applied to this layer is a 2D motionvector Pass.

I render out a 3×32 bit Normal Float openEXR.

But if i look at the openEXR i only get a image with a gentle gradient from left to right in the red channel of the motionvector Channel Layer.

However this method is working for the Depth Pass

What am i doing wrong here?

Can anybody help?

Greetings

Mitch Braggart