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Grant Tompkins asked ·

Alembic liquid with motion blur from XP OpenVDB Mesher

After caching and baking a liquid mesh sequence to alembic from an XP OpenVDB Mesher the mesh disappears when motion blur is enabled. I’m using the velocity vertex maps in the corresponding Arnold tag fields but nothing is working. Happens in both IPR and render output.

motion bluralembic
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Do you see any error messages in the console log? Would it be possible to share the files?

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The console output : Not sure what it means. Screenshot attached.

[c4dtoa] 00:00:02 2496MB WARNING | resetting parameter vlist on /xpOVDBMesher|xpOVDBMesher (found: nans or infs)

screen-shot-2021-03-01-at-50055-pm.png


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It means the vertex list (vlist) has bad values in it. So the vertex list was reset to its default value, which means no vertices.


NaN is "not a number", a value that cannot be represented as a floating point number on a computer.

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Grant Tompkins answered ·

Got it working. Can't say for sure which thing fixed it, but here's my guess :


1. Disabled XP Thinking Particles generation. Was testing out the XP OVDB Mesher vs Realflow for C4D mesher which needs a TP group. Re-Cache XP after disabling. There's always been mismatched coordinate problems with XP and generated TP, so this might have resulted in corrupted data which showed up as blue spots on the vertex tag for Velocity X.


2. XP OVDB Mesher creates 3 velocity vertex maps and a 4th vertex color map with RGB velocity data. This is the one that worked, but only when using the "vector(color)" and "by name" options and manually copying and pasting the vertex color tag name. Using the "link" method has never worked.


3. Edit : It's probably the smoothing filters of the OVDB Mesher. Adjusting them before bake introduced the blue spots into the Velocity X vertex map when the voxel size was below 2 and the smoothing iterations were above 1. Managed to find a sweet spot with Voxel size at 2 using the Mean filter method. The Smoothing deformer also does a decent job and leaves the vertex maps alone.

Hope this helps anyone else running into the same problem.


screen-shot-2021-03-01-at-94559-pm.png


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