Alembic does not import children of cameras correctly #73269

New Issue

Vincent Girès · 2020-01-20T17:37:50+01:00

Vincent Girès commented

2020-01-20 17:37:50 +01:00

System Information
Operating system: Linux-3.10.0-327.el7.x86_64-x86_64-with-centos-7.2.1511-Core 64 Bits
Graphics card: GeForce GTX 1070 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 390.77

Blender Version
Broken: version: 2.81 (sub 16), branch: master, commit date: 2019-11-20 14:27, hash: 26bd5ebd42

Short description of error
Alembic does not import object inside a group correcty

Exact steps for others to reproduce the error
Import this alembic file cam_from_maya_raw.abc in blender and you can see the problem which is not there on maya or nuke.

It should be aligned like that:

Maya

Nuke

**System Information** Operating system: Linux-3.10.0-327.el7.x86_64-x86_64-with-centos-7.2.1511-Core 64 Bits Graphics card: GeForce GTX 1070 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 390.77 **Blender Version** Broken: version: 2.81 (sub 16), branch: master, commit date: 2019-11-20 14:27, hash: `26bd5ebd42` **Short description of error** Alembic does not import object inside a group correcty **Exact steps for others to reproduce the error** Import this alembic file [cam_from_maya_raw.abc](https://archive.blender.org/developer/F8289930/cam_from_maya_raw.abc) in blender and you can see the problem which is not there on maya or nuke. ![abc_bug_report_blender.png](https://archive.blender.org/developer/F8289931/abc_bug_report_blender.png) It should be aligned like that: Maya ![abc_bug_report_maya.png](https://archive.blender.org/developer/F8289933/abc_bug_report_maya.png) Nuke ![abc_bug_report_nuke.png](https://archive.blender.org/developer/F8289938/abc_bug_report_nuke.png)

Vincent Girès commented

2020-01-20 17:37:50 +01:00

Added subscriber: @VincentGires

Vincent Girès changed title from ~~Alembic does import object inside a group correcty~~ to Alembic does not import object inside a group correcty

2020-01-20 21:56:50 +01:00

Philipp Oeser commented

2020-02-11 15:51:38 +01:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2020-02-11 15:51:38 +01:00

Changed status from 'Needs Triage' to: 'Confirmed'

Philipp Oeser commented

2020-02-11 15:51:38 +01:00

Can confirm the behavior.
Not sure how this looks from the inside, will check abcecho...

Can confirm the behavior. Not sure how this looks from the inside, will check `abcecho`...

Sybren A. Stüvel commented

2020-02-13 15:44:29 +01:00

Added subscriber: @dr.sybren

Sybren A. Stüvel self-assigned this 2020-02-13 15:44:29 +01:00

Sybren A. Stüvel commented

2020-02-13 15:44:29 +01:00

In the example Alembic file there are three cameras in a hierarchy. CAM_C is the parent, with children CAM_R and CAM_L.

On top of the whole Y=up (Alembic) vs. Z=up (Blender), cameras in Alembic have a different coordinate system than cameras in Blender. After the conversion to Blender's Z=up, this difference remains:

Blender camera: looks towards -Z by default
Alembic camera: looks towards -Y by default

As a result, we have to apply yet another rotation to get the cameras to match; let's call this the "correction rotation". This is done for every Alembic camera, and as a result the children of such a camera are rotated as well. This is what you see when importing the example file.

I think the solution would be to put the inverse of this rotation in the inverse parent matrix of any object that is a child of a camera.

In the example Alembic file there are three cameras in a hierarchy. `CAM_C` is the parent, with children `CAM_R` and `CAM_L`. On top of the whole Y=up (Alembic) vs. Z=up (Blender), cameras in Alembic have a different coordinate system than cameras in Blender. After the conversion to Blender's Z=up, this difference remains: - Blender camera: looks towards `-Z` by default - Alembic camera: looks towards `-Y` by default As a result, we have to apply yet another rotation to get the cameras to match; let's call this the "correction rotation". This is done for every Alembic camera, and as a result the children of such a camera are rotated as well. This is what you see when importing the example file. I think the solution would be to put the inverse of this rotation in the inverse parent matrix of any object that is a child of a camera.

blender-admin commented

2020-02-14 15:21:19 +01:00

This issue was referenced by 7c5a44c71f

This issue was referenced by 7c5a44c71f13ef00067f5c5951a275eb2eab2eef

Sybren A. Stüvel commented

2020-02-14 15:43:01 +01:00

Changed status from 'Confirmed' to: 'Resolved'

Sybren A. Stüvel closed this issue

2020-02-14 15:43:01 +01:00

Sybren A. Stüvel changed title from ~~Alembic does not import object inside a group correcty~~ to Alembic does not import children of cameras correctly

2020-02-14 15:44:34 +01:00

Vincent Girès commented

2020-02-17 14:24:43 +01:00

Thank you. This is working great in the last build and also for geometry shapes!

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Alembic does not import children of cameras correctly #73269