Scaling issues between Maya and Houdini

[Kacey Coley]

Hello everyone.  In our studio at university, we wish to use alembic to transfer animation data from Maya to Houdini so the effects artists could work with the assets for their simulations.  However, we've found that the alembic scene seems to scale itself to about 200 times its original size when transferred from Maya to Houdini.  Several forums have suggested simply scaling the models to 0.1 or 0.01 in Houdini to solve the issue, though we wonder if there is a better solution, especially ones that can work with custom scene units in either application.  At the moment, we've discussed implementing a digital asset that automatically scales the alembic file when brought into Houdini.  We also thought of exporting metadata in the alembic file from Maya and using a transformation when brought into Houdini to convert it to Houdini units.  Does anyone know of a better workflow for this process or knows of a clean solution?

Your answers are appreciated and I apologize if this has been answered elsewhere.

~Kacey

[Francois Chardavoine]

This is likely a difference in default units between your two apps - it sounds like one is in centimeters and the other in meters?

Can you make sure both apps are set to the same thing?
Francois.

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[Steven Shapiro]

I sent a longer reply, but it looks like it went into the ether.  Basically, I don't recommend changing the in application unit of measurement (in Maya or Houdini).  Scaling, in my opinion, is currently the best option partially because of transparency.  If you are going to scale, I recommend storing the unit of measurement as a property in the alembic cache (or in an asset management system), like 'meters', so you can determine the scale factor of that geometry into your current unit of measurement in the app you are using the geometry.

-Steve

[Kacey Coley]

Thank you Francois and Steven!

   
 Francois, we had the Maya scene set to centimeters and the houdini scene set to meters, though the maya scene, when imported into Houdini, was still rather large.  To get it to match Maya, we scaled the Houdini alembic scene by 0.5.  I also made both applications the same unit (meters), but we had to scale the cube to 0.005 when brought into Houdini to match Maya's scale.  I suppose if we set a standard for the scaling, then the scaling factor could manually be entered with this method, though the challenge would be to calculate the scaling factor any time Houdini or Maya's scale units are changed.  We may start with this approach just to get the effects generated.

Steven, that is a good point about having the scaling separate from the application.  We currently are working on a database system for managing our assets, and we could introduce an attribute pertaining to the scale of the alembic scene data to determine the appropriate scale factor.  Alternatively, we can try to find a way to store the unit of measurement into the alembic cache from Maya, so we can dynamically calculate the scale when imported into Houdini.

Again, thanks for the feedback, and it will be helpful with developing our pipelines!

~Kacey

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Kacey Coley
Digital Production Arts, M.F.A.
Clemson University