The Complete USD to glTF Conversion Guide

General Information

This guide is part of the RapidPipeline 3D Formats Knowledge Database. It shows how to convert USD to glTF, if you'd like to know more about the formats, please check out the following links:

• Learn more about the USD format
• Learn more about the glTF format
• Limitations of a USD Files to glTF Conversion Workflow

What are USD and glTF files commonly used for?

The USD file is a format mostly used for 3D modeling and rendering applications, and exchange of 3D authoring data.
The glTF file is a format mostly used for interactive 3D, on the Web and elsewhere (e.g., in XR).

Limitations of a USD Files to glTF Conversion Workflow

The following limitations should be taken into account when converting USD files to glTF format:

USD Feature (not supported by glTF)	Limitation Details
Free-Form Surfaces	Free-Form Surfaces: supported in USD, but not in glTF. Free-form surfaces allow a CAD user to design surfaces with advanced controls over curvature and continuitiy. While these surfaces are common for CAD models (in the form of so-called boundary representations or "B-reps"), they need to be converted to polygonal triangle or quad data to work with most 3D rendering engines - a process called tessellation. In this example, a surface patch is used to describe a part of a curved surface of a product. Without support for this feature, the free-form surface has to be tessellated into quads or triangles.
Quad Meshes	Quad Meshes: supported in USD, but not in glTF. Quad meshes are a common way to hand-model and edit 3D models. 3D artists get intuitive control and such meshes are also easy to refine, as well as well-suited for creation of skinned animations. However, real-time rendering pipelines and hardware are usually all based on triangles, so if a 3D model should not be edited any more, it is safe to convert quads to triangles (and engines will do this automatically before sending data to the rendering hardware). In this example, a part of a mesh is modeled with quads. Without support for this feature, quads will have to be triangulated, producing a pure triangle mesh.
Procedural Textures	Procedural Textures: supported in USD, but not in glTF. Procedural texture allow the modeling of surface details through mathematical functions, along with artistic control over various parameters. Typically, they are used for patterns like wood grain or other semi-regular structures. Since they are not using any pixels as source data, procedural textures have, in principle, infinite resolution and are very lightweight to describe. In this example, a procedural texture is used to model the look of a wooden material. Without support for this feature, in this case, the wooden parts won't show any visible details.
Scene Composition	Scene Composition: supported in USD, but not in glTF. Scene Composition describes the process of composing a scene through links from a main scene that pull in various other scenes/3D models. This can also happen in a nested fashion (through multiple levels of linkage). With a target format not supporting this feature, references to external models must be resolved and the content be baked into one 3D model, which is then saved in that target format.

Converting and Optimizing USD Files to glTF

There are various ways to convert between USD and glTF. With RapidPipeline, you can easily convert and and optimize USD files, at scale. It supports glTF, as well as many other file formats (examples: 3dsMax, FBX, OBJ, PLY, STEP, STL, USDZ, VRM), at high quality.

Due to the potential limitations aforementioned on the table above, in principle, one cannot always perfectly convert 3D data between glTF and other formats. In the following, you can find conversion guides between glTF and the most important other formats, along with a rough score for compatibility of this workflow:

What's the best way to get USD files into my 3D applications, and are there alternatives to using glTF?

Doing 3D conversion right, especially at scale, can be tricky, as 3D data is in general a rather complex (yet very powerful!) medium. This also applies to USD and glTF files - the conversion guide above provides a rough first idea about that. Once you know what you would like to do, tools like RapidPipeline can help you perform the necessary steps, and to even automate the process for thousands or even millions of files.

Especially when introducing pipelines and workflows at scale in an enterprise context, it is usually good to rely on dedicated tools and expertise, making sure you do not introduce any steps into your 3D workflow that are detrimental to the final output's quality, or that take your team too much time (and money).

If you're interested to hire dedicated expertise from the best in the field to help your company reach your goals fast and reliably, please do not hestitate to contact DGG. Being the creators of RapidPipeline, and ambassadors for open 3D standards for more than a decade, we have been building some of the world's most advanced 3D pipelines, having processed many millions of 3D assets.

Therefore, our expertise will help you to reach your goals faster, at scale, and with the least possible friction, since we are focused on maximum interoperability.

To get started with 3D data conversion and optimization today, sign up for a free account!

If you have any questions, feel free to chat with our human team.