Alembic import - Incorrect object pivots #70408

New Issue

Jani Kahrama · 2019-10-01T07:20:18+02:00

Jani Kahrama commented

2019-10-01 07:20:18 +02:00

System Information
Operating system: Darwin-18.7.0-x86_64-i386-64bit 64 Bits
Graphics card: AMD Radeon R9 M370X OpenGL Engine ATI Technologies Inc. 4.1 ATI-2.11.20

Blender Version
Broken: version: 2.81 (sub 12), branch: master, commit date: 2019-09-22 20:38, hash: 52bdf522af
Worked: (optional)

Short description of error
Alembic import places pivots of objects at origin, ignoring object pivot data in the file.

Exact steps for others to reproduce the error
Import pivot_debug.abc in Blender
Observe pivots of all objects at 0, 0, 0
Compare to pivot_debug_expectedresult.jpg

When pivot_debug.abc is imported back into Maya, the pivots are in their expected locations.

pivot_debug.abc

**System Information** Operating system: Darwin-18.7.0-x86_64-i386-64bit 64 Bits Graphics card: AMD Radeon R9 M370X OpenGL Engine ATI Technologies Inc. 4.1 ATI-2.11.20 **Blender Version** Broken: version: 2.81 (sub 12), branch: master, commit date: 2019-09-22 20:38, hash: `52bdf522af` Worked: (optional) **Short description of error** Alembic import places pivots of objects at origin, ignoring object pivot data in the file. **Exact steps for others to reproduce the error** Import pivot_debug.abc in Blender Observe pivots of all objects at 0, 0, 0 Compare to pivot_debug_expectedresult.jpg When pivot_debug.abc is imported back into Maya, the pivots are in their expected locations. ![pivot_debug_expectedresult.jpg](https://archive.blender.org/developer/F7783145/pivot_debug_expectedresult.jpg) [pivot_debug.abc](https://archive.blender.org/developer/F7783148/pivot_debug.abc)

Jani Kahrama commented

2019-10-01 07:20:18 +02:00

Added subscriber: @Frand

Philipp Oeser commented

2019-10-02 11:06:56 +02:00

Added subscribers: @dr.sybren, @lichtwerk

Sybren A. Stüvel was assigned by Philipp Oeser

2019-10-02 11:06:56 +02:00

Philipp Oeser commented

2019-10-02 11:06:56 +02:00

Not sure about this.

Blender seems to be able to preserve pivot points just fine.
If I import pivot_debug.abc into an empty scene, select all meshes, do Object > Set Origin > Origin To Geometry and export as alembic again, I end up with
#70408.abc
We can also remove the parent empty for clarity:
T70408_no_parentempty.abc
If I import that, pivots are preserved just fine.

Now what is the difference between pivot_debug.abc and #70408.abc?
We can look at it with abcls

./abcls -a -v -r pivot_debug.abc 
/:
wood_stand   .childBnds   Box((-0.576641, -1.78814e-07, -0.513623), (0.576641, 1.20603, 0.513623))
statistics   PolyStaticNum 9 PolyStaticCVs 1698 PolyStaticFaces 1680 TransStaticNum 10 
1.samples   1

/wood_stand:
wood_stand_part1   wood_stand_part2   wood_stand_part3   wood_stand_part4   wood_stand_part5   wood_stand_part6   wood_stand_part7   wood_stand_part8   wood_stand_part9   .xform   

/wood_stand/wood_stand_part1:
wood_stand_partShape1   .xform   
/wood_stand/wood_stand_part1/.xform:
.inherits   1
.ops   19, 19, 17, 17
.vals   -0.491225, 0.387752, -0.0152625, 0.491225, -0.387752, 0.0152625, -0.491225, 0.387752, -0.0152625, 0.491225, -0.387752, 0.0152625
isNotConstantIdentity   1

./abcls -a -v -r T70408.abc 
/:
wood_stand   .childBnds   Box((-0.576641, -1.78814e-07, -0.513623), (0.576641, 1.20603, 0.513623))

/wood_stand:
wood_stand_part1   wood_stand_part2   wood_stand_part3   wood_stand_part4   wood_stand_part5   wood_stand_part6   wood_stand_part7   wood_stand_part8   wood_stand_part9   .xform   visible   1

/wood_stand/.xform:
.inherits   0
.ops   48
.vals   1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1

/wood_stand/wood_stand_part1:
wood_stand_part1Shape   .xform   visible   1

/wood_stand/wood_stand_part1/.xform:
.inherits   1
.ops   48
.vals   1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, -0.491225, 0.38778, 0.0128468, 1
isNotConstantIdentity   1

./abcls -a -v -r T70408_no_parentempty.abc 
/:
wood_stand_part1   wood_stand_part2   wood_stand_part3   wood_stand_part4   wood_stand_part5   wood_stand_part6   wood_stand_part7   wood_stand_part8   wood_stand_part9   .childBnds   Box((-0.576641, -1.78814e-07, -0.513623), (0.576641, 1.20603, 0.513623))

/wood_stand_part1:
wood_stand_part1Shape   .xform   visible   1

/wood_stand_part1/.xform:
.inherits   0
.ops   48
.vals   1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, -0.491225, 0.38778, 0.0128468, 1
isNotConstantIdentity   1

@dr.sybren: I assume this is about the different XFormOps ? Is there a resource where we can find out about these used values [we: 48, them: 19, 19, 17, 17]
(couldnt find anything on https://docs.alembic.io/search.html?q=Xform)

Not sure about this. Blender seems to be able to preserve pivot points just fine. If I import `pivot_debug.abc` into an empty scene, select all meshes, do `Object` > `Set Origin` > `Origin To Geometry` and export as alembic again, I end up with [#70408.abc](https://archive.blender.org/developer/F7785375/T70408.abc) We can also remove the parent empty for clarity: [T70408_no_parentempty.abc](https://archive.blender.org/developer/F7785379/T70408_no_parentempty.abc) If I import that, pivots are preserved just fine. Now what is the difference between `pivot_debug.abc` and `#70408.abc`? We can look at it with `abcls` ``` ./abcls -a -v -r pivot_debug.abc /: wood_stand .childBnds Box((-0.576641, -1.78814e-07, -0.513623), (0.576641, 1.20603, 0.513623)) statistics PolyStaticNum 9 PolyStaticCVs 1698 PolyStaticFaces 1680 TransStaticNum 10 1.samples 1 /wood_stand: wood_stand_part1 wood_stand_part2 wood_stand_part3 wood_stand_part4 wood_stand_part5 wood_stand_part6 wood_stand_part7 wood_stand_part8 wood_stand_part9 .xform /wood_stand/wood_stand_part1: wood_stand_partShape1 .xform /wood_stand/wood_stand_part1/.xform: .inherits 1 .ops 19, 19, 17, 17 .vals -0.491225, 0.387752, -0.0152625, 0.491225, -0.387752, 0.0152625, -0.491225, 0.387752, -0.0152625, 0.491225, -0.387752, 0.0152625 isNotConstantIdentity 1 ``` ``` ./abcls -a -v -r T70408.abc /: wood_stand .childBnds Box((-0.576641, -1.78814e-07, -0.513623), (0.576641, 1.20603, 0.513623)) /wood_stand: wood_stand_part1 wood_stand_part2 wood_stand_part3 wood_stand_part4 wood_stand_part5 wood_stand_part6 wood_stand_part7 wood_stand_part8 wood_stand_part9 .xform visible 1 /wood_stand/.xform: .inherits 0 .ops 48 .vals 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1 /wood_stand/wood_stand_part1: wood_stand_part1Shape .xform visible 1 /wood_stand/wood_stand_part1/.xform: .inherits 1 .ops 48 .vals 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, -0.491225, 0.38778, 0.0128468, 1 isNotConstantIdentity 1 ``` ``` ./abcls -a -v -r T70408_no_parentempty.abc /: wood_stand_part1 wood_stand_part2 wood_stand_part3 wood_stand_part4 wood_stand_part5 wood_stand_part6 wood_stand_part7 wood_stand_part8 wood_stand_part9 .childBnds Box((-0.576641, -1.78814e-07, -0.513623), (0.576641, 1.20603, 0.513623)) /wood_stand_part1: wood_stand_part1Shape .xform visible 1 /wood_stand_part1/.xform: .inherits 0 .ops 48 .vals 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, -0.491225, 0.38778, 0.0128468, 1 isNotConstantIdentity 1 ``` @dr.sybren: I assume this is about the different XFormOps ? Is there a resource where we can find out about these used values [we: 48, them: 19, 19, 17, 17] (couldnt find anything on https://docs.alembic.io/search.html?q=Xform)

Jani Kahrama commented

2019-10-02 11:13:13 +02:00

The objects are exported from Maya 2019.1, please let me know if there are specific test objects you'd like me to generate.

Jani Kahrama commented

2019-10-02 11:29:48 +02:00

Attached is the case of a cube with the pivot manually set to the center of its top face. The file imports back to Maya with the pivot in the same location.

testCube.abc

Attached is the case of a cube with the pivot manually set to the center of its top face. The file imports back to Maya with the pivot in the same location. ![pivotCube.PNG](https://archive.blender.org/developer/F7785424/pivotCube.PNG) [testCube.abc](https://archive.blender.org/developer/F7785423/testCube.abc)

Philipp Oeser commented

2019-10-02 11:54:05 +02:00

This is abcls for that file (still assume it has to do with the .ops part of the XForm?)

./abcls -a -v -r testCube.abc 
/:
pCube1   .childBnds   Box((-0.5, 0, -0.5), (0.5, 1, 0.5))
statistics   PolyStaticNum 1 PolyStaticCVs 8 PolyStaticFaces 6 TransStaticNum 1 
1.samples   1

/pCube1:
pCubeShape1   .xform   
/pCube1/.xform:
.inherits   1
.ops   19, 19, 17, 17
.vals   0, 1, 0, -0, -1, -0, 0, 1, 0, -0, -1, -0
isNotConstantIdentity   1

This is `abcls` for that file (still assume it has to do with the `.ops` part of the XForm?) ``` ./abcls -a -v -r testCube.abc /: pCube1 .childBnds Box((-0.5, 0, -0.5), (0.5, 1, 0.5)) statistics PolyStaticNum 1 PolyStaticCVs 8 PolyStaticFaces 6 TransStaticNum 1 1.samples 1 /pCube1: pCubeShape1 .xform /pCube1/.xform: .inherits 1 .ops 19, 19, 17, 17 .vals 0, 1, 0, -0, -1, -0, 0, 1, 0, -0, -1, -0 isNotConstantIdentity 1 ```

Philipp Oeser commented

2019-10-02 12:25:11 +02:00

Only thing I can think of is we are not hadling (more or less a stab in the dark...)

Alembic::AbcGeom::kScalePivotPointHint
Alembic::AbcGeom::kRotatePivotPointHint

https://github.com/alembic/alembic/blob/master/maya/AbcImport/XformHelper.cpp

@dr.sybren: does this ring a bell?

Only thing I can think of is we are not hadling (more or less a stab in the dark...) `Alembic::AbcGeom::kScalePivotPointHint` `Alembic::AbcGeom::kRotatePivotPointHint` https://github.com/alembic/alembic/blob/master/maya/AbcImport/XformHelper.cpp @dr.sybren: does this ring a bell?

Sybren A. Stüvel commented

2019-10-02 13:00:21 +02:00

Changed status from 'Open' to: 'Archived'

Sybren A. Stüvel closed this issue

2019-10-02 13:00:21 +02:00

Sybren A. Stüvel commented

2019-10-02 13:00:21 +02:00

Blender simply uses the transformation matrix of each object, which is constructed from the Alembic file by the Alembic library itself (source). The Alembic file can contain various separate operations, or the final matrix. In the case of this Maya-generated file, it contains a sequence of operations. This is such a sequence:

XForm .xform contains 4 operations:
  - type 1  Translate -0.491225, 0.387752, -0.015263
  - type 1  Translate 0.491225, -0.387752, 0.015263
  - type 1  Translate -0.491225, 0.387752, -0.015263
  - type 1  Translate 0.491225, -0.387752, 0.015263
OBwood_stand_part1
1.000000 0.000000 0.000000 0.000000
0.000000 1.000000 0.000000 0.000000
0.000000 0.000000 1.000000 0.000000
0.000000 0.000000 0.000000 1.000000

As you can see, the transformations cancel each other out, and result in a unity matrix. The same you can see in the cube example.

Maya has a pivot point that is separate from the object origin, and it encodes this pivot point in the transform operations. Blender doesn't have a separate per-object pivot point, so we cannot load this information. To use the pivot point as object origin, bake the pivot points in Maya and then export to Alembic.

Closing this as 'Invalid' as this does not constitute a bug in Blender.

Blender simply uses the transformation matrix of each object, which is constructed from the Alembic file by the Alembic library itself ([source](https://github.com/alembic/alembic/blob/8bf5f3494ead3ccb8820fd1768d3f8c764e43fb9/lib/Alembic/AbcGeom/XformSample.cpp#L550)). The Alembic file can contain various separate operations, or the final matrix. In the case of this Maya-generated file, it contains a sequence of operations. This is such a sequence: ``` XForm .xform contains 4 operations: - type 1 Translate -0.491225, 0.387752, -0.015263 - type 1 Translate 0.491225, -0.387752, 0.015263 - type 1 Translate -0.491225, 0.387752, -0.015263 - type 1 Translate 0.491225, -0.387752, 0.015263 OBwood_stand_part1 1.000000 0.000000 0.000000 0.000000 0.000000 1.000000 0.000000 0.000000 0.000000 0.000000 1.000000 0.000000 0.000000 0.000000 0.000000 1.000000 ``` As you can see, the transformations cancel each other out, and result in a unity matrix. The same you can see in the cube example. Maya has a pivot point that is separate from the object origin, and it encodes this pivot point in the transform operations. Blender doesn't have a separate per-object pivot point, so we cannot load this information. To use the pivot point as object origin, [bake the pivot points](https://knowledge.autodesk.com/support/maya/learn-explore/caas/CloudHelp/cloudhelp/2018/ENU/Maya-Basics/files/GUID-378D7FF6-492F-4DA4-A468-507E6ABF8B58-htm.html) in Maya and then export to Alembic. Closing this as 'Invalid' as this does not constitute a bug in Blender.

Jani Kahrama commented

2019-10-02 13:00:52 +02:00

In #70408#787609, @lichtwerk wrote:
Only thing I can think of is we are not hadling (more or less a stab in the dark...)

Alembic::AbcGeom::kScalePivotPointHint
Alembic::AbcGeom::kRotatePivotPointHint

https://github.com/alembic/alembic/blob/master/maya/AbcImport/XformHelper.cpp

@dr.sybren: does this ring a bell?

In Maya, I do notice the pivot point referred to as RotationPivot, so this may very well be it.

> In #70408#787609, @lichtwerk wrote: > Only thing I can think of is we are not hadling (more or less a stab in the dark...) > > `Alembic::AbcGeom::kScalePivotPointHint` > `Alembic::AbcGeom::kRotatePivotPointHint` > > https://github.com/alembic/alembic/blob/master/maya/AbcImport/XformHelper.cpp > > @dr.sybren: does this ring a bell? In Maya, I do notice the pivot point referred to as RotationPivot, so this may very well be it.

Philipp Oeser commented

2019-10-02 13:08:58 +02:00

thx for learing that up @dr.sybren

Jani Kahrama commented

2019-10-02 16:32:53 +02:00

Thank you for the explanation, baking pivots in Maya resolves our problem.

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Alembic import - Incorrect object pivots #70408