Smoke motion blur from alembic

[nico_venster]

I am having a problem with getting continuous smoke emitting from an object. The emitter object is parented to an imported (and animated) alembic file which is moving quite fast. To try and rectify this I watched Peter Quint's videos on smoke in H12, and in the second video (the part on moving objects and motion blur) he mentions that to activate motion blur the animation (of the emitter object) should be on geometry level as opposed to the scene level.

 

Could it be that my motion blur (and essentially continuous smoke) is not working because the animation is coming from the alembic file? And if there is another way to get continuous smoke emitting from a fast moving object (like smoke "substeps") please let me know =/

 

Thanks!

[nico_venster]

I have attached my H file with a proxy sphere basically animated on the path of the alembic source for added reference or insight.

smoke.hipnc

[fathom]

motion blur is really a rendering thing.  if i understand what your problem is, it's more about the classic problem of a fast emitter dropping clumps of particles/smoke into a sim at discrete time slices.

 

depending on your alembic file, you might need to add subframe data.  you can use a timeblend sop (don't change the time or anything, but it will do blending between discrete frame samples).

now that's assuming you're doing a sim with enough subframes to capture the emitter's motion properly.

 

alternative B is to generate a volume that is elongated along the velocity vector to effectively bridge the gap between frames.  to do that, you'd make sure you've got good point velocities on your source geo, scatter a bunch of points on it, offset those points based on the velocity (wrangle: "v@P = v@P - v@v * f@TimeInc * float(rand(i@ptnum/5.67));" ), then generate a volume from those points using vdb tools (volume from particles for example).

 

you can certainly use both methods together as well.

[nico_venster]

Hi fathom, thanks for your help man. I appreciate the clarity regarding the motion blur and the old faithful smoke problem. I haven't worked with the timeblend sop before so moving through t he H example file a the moment. With regards to the subframes I hope I'm working with enough of them to use the emitter's motion.

 

Your point velocity solution seems interesting, although I'm still not doing something right and it might be something different all-together. I've got to be honest I'm not sure what the highlighted box in the screenshot is

 

[Peter Quint]

The motion blur referred to in the video is built in to the fluid source node. It is not in this case to do with rendering. It implements the elongation of volume along the velocity similar to that described above without the hassle of building it yourself.  To work the motion needs to be at the object level, not at the scene level. Here your parented animation is as I understand it at the scene level (I've not checked your file) Lay down a new geo node, dive inside delete the file node, and lay down an object merge. Set the transform to 'into current geometry' and then merge your source geo. You can then add a fluid source and get the right result.  

 

Peter

Edited September 5, 2015 by Peter Quint

[nico_venster]

Hi Peter, thank you for the clarification!

[chrsaenz]

Hi Peter,
I have watched your video and used the volume elongation along velocity with great results before... I used an object merge to create a fluid source from primitive spheres I placed inside a Rivet which followed the alembic object, this worked out great and could use the volume motion blur and with just 2 Sub Steps got a really good sim.
But is there a way to use this approach with a deforming Alembic Import?
What would be the simplest approach to bring the Alembic's Animation unto the Object Level?

Thanks!