Tuesday, October 15th, 2013 Posted by Jim Thacker

Pixar’s USD system: the new super-Alembic?


Pixar’s homepage graphic for its Universal Scene Description: Pixar is considering open-sourcing the system, which makes it easier to exchange data about the structure of entire production scenes between pipeline tools.

Pixar has posted some interesting information on its website about its Universal Scene Description (USD) system, used on its last three movies, and intended as a higher-level counterpart to Alembic.

In slides from a presentation at Siggraph 2013, the studio notes that Alembic “provides [interoperability between 3D applications] for geometry and materials. We see a need for a higher-level scene description standard”.

Like Alembic, but for entire scenes
USD builds on the same concepts as, and integrates with, Alembic, but is geared towards describing the structure of entire scenes, rather than individual assets.

Pixar notes: “While Alembic provides a good solution for representing flat, baked scene description, because it has no facility for file-referencing or sparse overrides, it cannot be our unified basis for pipeline data.”

Instead, the Universal Scene Description system supports scene-composition features like layering, referencing, and geometry and shading variants for individual assets.

Rather than acting as a replacement for Alembic, Pixar points out that the Universal Scene Description builds upon and extends the file format, noting that USD “leverage[s] Alembic archives as they are produced today”.

“This does not preclude a future in which Alembic and USD merge into a single entity [but] until that time, native Alembic files can … serve as the inputs to the referencing operators in USD.”

Very nice. So when can I use it?
While the idea of a new ‘super Alembic’ may be attractive, it’s only of academic interest unless your own tools support it.

In its Siggraph slides, Pixar notes that it is “gauging interest to determine if we want to release USD and its associated IP as an open-source project”.

To judge by the discussions the online material has sparked in industry forums today, the interest is certainly there. It will be interesting to see if Siggraph goes further with an open-source release.

Visit Pixar’s webpage about Universal Scene Description

View the slides from Pixar’s Siggraph 2013 presentation
(A lot more technical detail, and interesting performance stats from Pixar’s recent short The Blue Umbrella)