Motion Vectors problem with Arnold

[MaxGyver]

Hi

 

I'm trying to render a motion vector pass with Arnold.

 

Everything is fine as long as I try to have a Transformation Blur, but as soon as I try to get some Deformation Blur, no blur is detected.  My Arnold Shader Network look like this :

 

Motion Vector ---> OUT_Material

 

Geometry Velocity Blur is activated on my geometry.

 

Specs:

CentOS release 6.6 final

Houdini 14.0.201.13

Arnold 1.3.0

 

 

I tried different ways to deform a torus.  xform is working.  Moving points with a Point SOP don't.  Animating a Mountain SOP works some times.

 

Any idea how to set that?

 

Thanks

Maxime

 

 

[michaelb-01]

In the Motion Blur tab in the Arnold attributes (on your geometry node) have you enabled "velocity blur"? And you are calculating velocity?

[MaxGyver]

Oh Yeah!

 

I'm new to Arnold.  Didn't add the Arnold Properties to my geometry node.  Now it seems to work.  Added a couple Trail SOP with compute velocity, and now it's fine.  But is there a way to compute those motion vectors without blurring the render.  Actually, my motion vector pass is an AOV, and as soon as I try to remove the blur from the render, my Motion Vector pass stop working properly.  I tried to set the shutter as explained in the Motion Vector documentation :

 

https://support.solidangle.com/display/AFHUG/Motion+Vector

 

But it seems I can't obtain the correct Motion vector pass without blurring the render.

 

 

Thanks

Maxime

[MaxGyver]

SOLVED!

 

The Shutter thing explained in the Arnold Motion Vector Node documentation is actually on the Arnold Properties added to the Camera.

[michaelb-01]

Glad you solved it. I'm not sure about Houdini but in Maya you can disable motion blur in the "Overrides" tab in the render globals. There is probably the same thing on the Arnold ROP node?

[MaxGyver]

Hi Michael

 

Yes, the Arnold ROP node in Houdini have an option to turn off Motion Blur, but when I turned it off, motion blur AND motion vectors were turned off.  The trick was to set the shutter directly on the Arnold properties on the geometry node.

 

 

Thanks

Maxime