Hi,

I have generate an particle animation and converted into fog with VDB from particles. I would like to generate velocity inputs of each voxel but I have no idea, I have tried to find a solution over online tutorials, but with no luck.

Is there a way to generate velocity inpus based on the position of each voxel? (because they are moving very fast)

Cheers

You cant generate a vel from just the fog volume, it makes no sense. You will need the original particles with a v attrib already calculated then just add the v attribute on the VDB From Particles node, or use a volume velocity node to create the vel from your points.

One of the features announced in 16.5 is volume optical flow, which can compute a vector field from a sequence of volumes or images.

Hi guys,

sorry for my dely on the reply… Today internet was offline in the office. Thanks for your replys.

JordanWalsh
You cant generate a vel from just the fog volume, it makes no sense. You will need the original particles with a v attrib already calculated then just add the v attribute on the VDB From Particles node, or use a volume velocity node to create the vel from your points.

Ok I see! thanks

Now I have another problem, I have create vdb from particles, I add the velocity att here, then I connect a cloud noise but the velocity is lost here… I suppose this node is incompatible with this workflow right?

jsmack
One of the features announced in 16.5 is volume optical flow, which can compute a vector field from a sequence of volumes or images.

Wow! that's sound amazing. Is there a tutorial to see how to use it properly?

Thanks for the info!

This example is just for a heightfield, but it should work the same for a 3d volume; take your volume, timeshift it by 1 frame, feed both those volumes to the optical flow sop, it'll generate a velocity field for you (which you might have to do some rename tricks to make a regular @vel to feed to other systems):

http://www.tokeru.com/cgwiki/index.php?title=HoudiniDops#Volume_Optical_Flow [www.tokeru.com]