How to make a velocity layer in hou13

[openan]

i want to make a velocity layer

Who can help me or give me scene .

thank you !

 

[cojoMan]

I was having the same question right now )

at the moment, I am rendering my usual passes in Houdini, then cache out and render the velocity in 3dsmax, MR, as I know the output there and how to use it...

it would be nice to do it in Houdini though

[whodini]

I wantto figure this out as well, I was digging around the sesi forums and found a topic a long time ago about how to hack a motion vector pass together.

[Guest tar]

Like the attached?

 

Add an parameter 'v' to the shader

 

Computer vel with trail in Sops

 

Turn on motion blur on the geo and mantra but turn it off for the render.

VelPass2.hip

[Netvudu]

hi Marty,

 

but that´s a velocity pass, not a motion vector pass, is it?

 

I mean, I´m still using the method of subtracting the GetBlurP from one frame of the previous one...I understand that´s still the current method?

 

Then again, it´s not clear what people wants. Some of them ask for velocity and others for a motion vector...

Edited May 21, 2014 by Netvudu

[cojoMan]

marty, Netvudu, could you possibly enlighten us on the motion vector pass as well ?

 

GetBlurP ?..

 

 

I mean, I´m still using the method of subtracting the GetBlurP from one frame of the previous one...I understand that´s still the current method?

 

[Guest tar]

Motion Vector and Velocity should be the same thing - GetBlurP is for Scene level motion IRRC.

 

http://www.sidefx.com/docs/houdini13.0/examples/nodes/out/ifd/MotionVector

 

http://www.sidefx.com/docs/houdini13.0/nodes/vop/getblurP

 

Edit: added screen capture of GetPBlur Vop setup from example

Edited May 21, 2014 by tar

[Neil78]

Here's a slight variation on a  theme to .......http://forums.odforce.net/topic/20233-motion-vector-pass-and-nuke-workflow/

[mrWolf]

Hi !

I hope this post is still alive

Given that the point velocity attribute is already on the geometry I am rendering, 

the way I've always exported my velocity pass is simply binding "v" into a mantra material builder, transforming from "world" to "camera" ("direction" mode) , sometimes multiplying by 1/24 and exporting.

 

In general I use this pass to add motion blur in comp via Nuke, and it seems to work quite well.

 

I 've seen several threads about exporting velocity and I am pretty sure I am missing something, cause in general people use more elaborated ways to do that.

[Serg]

There is an issue with this, in that the camera velocity is not taken into account... This a problem if the camera is moving with the object, and numerous other situations ... on my list of things to look at properly, but I think it will probably involve sidefx support/fix. Its a problem whether you are exporting vectors or even rendering 3d blur.

[mrWolf]

hi Serg !

that makes sense ! You just made me realize that I've used that technique always in shots where the camera was still or moving very slowly.