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Alembic export do scale when rotating more than 360`
Closed, ArchivedPublic


System Information
Linux and windows

Blender Version
Blender v2.79b

Short description of error
If you rotate a armature's bone with an object parent to it more than 360` and you export the object as alembic file.
If you read the abc file in other software (test with maya, 3dsmax, houdini, guerilla) the object get a scale transformation.

Exact steps for others to reproduce the error

Thanks !

Event Timeline

Dont have access to other software atm., reads back fine into blender though.
abcview shows more or less nothing for me...

Does this also happen when you use the Flatten Hierarchy option in blenders abc exporter?

Bastien Montagne (mont29) lowered the priority of this task from 90 to Normal.Jul 22 2018, 5:45 PM
Sybren A. Stüvel (sybren) changed the task status from Unknown Status to Unknown Status.EditedAug 16 2019, 2:02 PM

I've done some digging, and it seems to be an issue with the reading applications. Both Gaffer and USDView show the wobbling scale issue. Exporting @colin (col-one)'s file with 24 FPS and then importing into Gaffer or USDView works fine. It's when there is a different frame rate that these programs fail.

It's not so much the large (> 360°) rotation that's the issue here, but rather the big rotational step from frame to frame. This makes it extra visible when programs interpolate incorrectly.

The hard-coded assumption of having 24 FPS can be seen in the USD sources, and I wouldn't be surprised if other software did this as well. It looks like the transformation matrices are linearly interpolated, which can cause these kind of artefacts. I filed bug report #940 at the USD tracker about this.