Velocity pass to Nuke

[billp]

Hello.
There is no documentation for implementing the Vray Velocity Render element.
I have searched the forums and there is conflicting comments of flipping the green, inverting red&green, setting to forward etc.

Can Chaos group provide some information on how this is supposed to work ?
I have tried numerous combination and none seem correct.

For example, should we use forward channel or motion ?
Should we use red & green ? Or red & blue ? For U, V
I have found that if I use red & green as recommended, any velocity that is blue obtains no vector blur and looks weird.
So I have used red & blue for the U,V. Though I am unsure if that looks right.

Any help appreciated !

[joconnell]

Right so. This is for max but should be the same in maya.

When you render from maya, add in the vray velocity element. The only thing you do to it is turn off clamp output.
When you get into nuke, feed your render directly into a vector blur node.
Set the uv channels to vray velocity.
Set the blur method to forward.
Make sure you set the alpha to the rgb.alpha or else you'll get a weird effect of a motion blurred and a sharp render faded together.

Then just use your multiply to control your motion blur amount. The number is the same as your blur duration in frames if you were to set it in the vray motion blur settings. 1 is 1 frame of motion blur, 0.5 is a half frame blur so that's what you'll mainly be using for vfx work.

Hope this helps!