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How to convert Universal Scene Description (.usd,.usda, .usdc.usdz) to COLLADA (.dae)?

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Universal Scene Description

The USD format (“Universal Scene Description”) is an open 3D model and scene format designed for efficient storage and streaming of 3D asset data. It is a high-performance extensible framework and ecosystem for describing, composing, simulating, and collaboratively navigating and constructing 3D scenes. An extensive overview of USD is provided in the Okino USD documentation.

Pixar Animation Studios originally created the USD platform (as its fourth generation variation after its Marionette & Preso systems) to improve studio-wide collaborative workflows. USD provides a concept of "scene composition", building a unified scene from potentially thousands of loosely-coupled source assets. For example, the mesh, rigging, materials, and animation for a single model might all come from different "layers" (files), each created and maintained by a different artist or department. Layers can store multiple "variants" of any given data, helping to solve problems of versioning/approval. The coupling between layers is very dynamic and loose, allowing for greater flexibility during the production process. The entire USD system is designed to facilitate a large studio making feature films, with all of the scale that that implies.

USD should be considered more of a code framework (“OpenUSD”) for use in group collaboration, to help with the aggregation of various 3D data sources into a unified scene through a process referred to as scene composition. A subset of that code framework provides for reading and writing USD disk-based files as well as rendering USD scenes (Hydra). The system is rather complex to implement (for software developers) and to use (from first principles) as a 3D graphics artist. The USD file format itself is not for faint of heart and is best read/written using the OpenUSD SDK + various programming APIs. More commonly used ASCII 3D file formats such as COLLADA, VRML2 and Wavefront OBJ are much easier to manipulate/understand/use on a human level basis.

File extensions used by the standard include:

• .usd, Either ASCII or binary-encoded
• .usda, ASCII encoded
• .usdc, Binary encoded
• .usdz, Zero-compression, unencrypted zip file

COLLADA

COLLADA (DAE) is a XML-based readable file format of the 2007/2008 era which had an original goal of allowing efficient cross conversion of 3D asset data between all of the major 3D DCC/Animation systems of that era. Many 3D software programs came to implement COLLADA but with varying levels of comformity and data reliability. COLLADA is more generally known as a polygonal mesh file format and not a MCAD/CAD/AEC/GIS format. Today people would usually use FBX over COLLADA, depending on the quality of the associated (and dated?) import/export converters.

Okino created one of the key implementations of the COLLADA file format in its import and export converters. However, it saw little need for them except for exporting into Cinema-4D from 2008 to 2012, as the primary gateway into Google Earth, and as our still-preferred method to move 3D assets into Blender (rather than FBX). COLLADA does have its place in these current and prior times.

Okino has a unique take on the COLLADA file format as Okino was at the very center of the DCC/Animation conversion world. In 2007 Rémi Arnaud and Mark Barnes argued that yet-another 3D file format was required and hence Sony funded their efforts to define COLLADA for the cross conversion of assets between (initially) 3ds Max and Maya. However, what they conveniently ignored was that Okino already had the defacto cross conversion system in place, for the prior decade, based on its BDF (binary data translation file format) for 3ds Max, Maya, Cinema-4D, Softimage, LightWave and others. In the mid 2000's there was a "not invented here" mindset and hence everyone wanted to stamp/force their own 3D file format on the industry: FBX (Autodesk), COLLADA (Sony), 3dxml (Dassault Systems), XAML-3D (Microsoft), U3D (Adobe and Intel), etc. There was little need or reason to have "yet-another" set of new 3D file formats. All, except FBX, would basically come and go as of 2007/2008. The implosion of the DCC/Animation industry of 2005-2007 and the 2008/2009 recession further hampered the long term adoption or need for COLLADA over Autodesk's FBX.

COLLADA is/was a very fine file format but it was really not needed at the time of its introduction in 2007. It only introduced yet-more confusion to the 3D graphics market as to which 3D file format to use to transfer 3D assets between packages. Developers generally implemented v1.4 of the COLLADA file specification then lost interest thereafter.

However, as a saving grace for COLLADA, all of the 3D software packages which had implemented a good COLLADA exporter became instant gateways to move their 3D assets into the then-new glTF file format of the mid 2010s, until such time that these same packages could add in their own glTF exporters.

Universal Scene Description import converter's overview

COLLADA export converter's overview