Transfering velocity from volume to polygons

[Muhc]

Hi folks!

 

I've done a sim of an rocket exhaust using smoke solver.

Using VDB tools I converted that smoke to polygons, due to art direction (catroon style project).

That mesh only has P attributes. The "vel.x", "vel.y" and "vel.z" are also present, but I imagine mantra needs "v" attribute on points to do geometry motion blur.

 

I'm not sure how to transfer vel fields to points.

 

My approach:

 

After meshing the smoke, I've put down a PointVOP

Inside PointVOP, I used three VolumeSample nodes to read the vel.x, vel.y and vel.z at the given point position.

I merged those volume samples into a vector and plug it in to "v" output.

 

It does give mi velocity on points, but when I render, there are artifacts present.

 

Can you suggest me another workflow for transfering velocity?

[Skybar]

What kind of artifacts? You can try the Attribute from Volume SOP, but you'll probably get the same.

[Muhc]

Oh, there is a SOP for that:) Didn't know it existed. Thanks!
It is doing what I want, but the artifacts remain. The artefacts are long motion blur streaks in different directions at the source emitter. I think it has to do with extreme velocities in smoke source. The funny thing is, when I render volume (before converting to polygons), there are no artefacts.
 
I attach .hipnc to clarify my problem.
 
Cheers!

Smoke_hoverboard.hipnc

Edited November 10, 2015 by Muhc

[Skybar]

It's probably because the mesh is sampling values at specific points in the velfield. If you are unlucky you might have two neighbouring points on your mesh with total opposite velocities. I tried smoothing the velfield (like you did with the density) and it looked better, not sure if it works for you though. You could try that. You can also Smooth SOP the v on your mesh. Maybe both together

[Muhc]

Thanks for ideas, will definitely try smoothing vel field.

[loudsubs]

Convert the vel field to a vdb along with density, and smooth both.

Smoke_hoverboard.hipnc