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Alembic export do scale when rotating more than 360` #55288

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opened 2018-06-01 15:53:58 +02:00 by colin · 5 comments
colin commented 2018-06-01 15:53:58 +02:00
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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.
blender_preview.gif
abc_preview.gif

Exact steps for others to reproduce the error
bug_rotation_scale_alembic.blend
bug_rotation_scale_alembic.abc

Thanks !

**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. ![blender_preview.gif](https://archive.blender.org/developer/F3544554/blender_preview.gif) ![abc_preview.gif](https://archive.blender.org/developer/F3544559/abc_preview.gif) **Exact steps for others to reproduce the error** [bug_rotation_scale_alembic.blend](https://archive.blender.org/developer/F3544571/bug_rotation_scale_alembic.blend) [bug_rotation_scale_alembic.abc](https://archive.blender.org/developer/F3544570/bug_rotation_scale_alembic.abc) Thanks !
colin commented 2018-06-01 15:53:58 +02:00
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Added subscriber: @col-one

Added subscriber: @col-one
Philipp Oeser commented 2018-06-06 12:54:57 +02:00
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Added subscriber: @lichtwerk

Added subscriber: @lichtwerk
Sybren A. Stüvel was assigned by Philipp Oeser 2018-06-06 12:54:57 +02:00
Philipp Oeser commented 2018-06-06 12:54:57 +02:00
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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?

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?
Sybren A. Stüvel commented 2019-08-16 14:02:39 +02:00
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Changed status from 'Open' to: 'Archived'

Changed status from 'Open' to: 'Archived'
Sybren A. Stüvel commented 2019-08-16 14:02:39 +02:00
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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 @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.

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 @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](https:*github.com/PixarAnimationStudios/USD/blob/32ca7df94c83ae19e6fd38f7928d07f0e4cf5040/pxr/usd/plugin/usdAbc/alembicReader.cpp#L961), 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](https:*github.com/PixarAnimationStudios/USD/issues/940) at the USD tracker about this.
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Reference: blender/blender#55288
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