Alembic: locations issue
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Description

System Information

Blender Version
2.78

Short description of error
I have exported alembic from houdini. But in blender it's imported with strange locations.
test.abc


Exact steps for others to reproduce the error
Import Alembic

Details

Type
Bug
Bastien Montagne (mont29) triaged this task as "Normal" priority.Jan 13 2017, 12:53 PM

@paul geraskin (mifth): Since I don't have Houdini to compare with, can you tell me which locations you expected to see in Blender, and which you are actually seeing? I understand that the clock should actually be on the tower, but having some concrete numbers will make things easier to reproduce & fix.

We just have to clear location of empty object named geo1 to obtain a coherent scene in blender.

Does this object have a different scale than the others in Houdini ?

I cannot see transforms in Houdini. Sorry.

But in Fusion I imported the file. Possibly it will help you somehow.
See Offset values.

And as was said by Ronan. If you clear position of this empty object - it will be ok.

In Houdini Geo1 is a house.

The issue most likely comes from the confusing logic that is used to convert data between Blender and Alembic, especially Alembic Y-up matrices to Blender Z-up ones. In the process, to create the Blender matrices, we multiply the matrices of the Alembic object with the one from its parent recursively, so maybe in this case the object matrix is somehow multiplied twice. The relevant function is in abc_util.cc.

I worked on, a few months ago, refactoring the Alembic importer to make use of a hierarchical tree like data-structure to more easily convert data between Blender and Alembic. It made the code easier to follow, and got rid of some special funky cases, but the matrices ended up being "corrupted" in some imported files which I didn't have the time to fully investigate, though chances are it was due to accumulating the same matrix over and over again.

Does it mean that problem occurs for every object with a negative Z location in Houdini ?

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