Advancing 3D Tiles and glTF in an Open Ecosystem

Amanda: We’re thrilled to welcome Don McCurdy to the Platform team at Bentley. I know Don through his work with open standards: he formerly co-chaired the 3D Formats working group responsible for glTF and created popular open source tools like glTF Transform. As the senior director of open standards at Bentley, vice chair of the Khronos 3D Formats working group, and co-chair of the Metaverse Standards Forum 3D Asset Interoperability working group, I’m passionate about the openness that standards enable. With an eye to the future of standards development, I sat down with Don and with Sean Lilley, who is a lead engineer behind 3D Tiles and a driving force in Cesium’s development, to talk about their contributions to open standards and what they see ahead as developers.

Amanda: Don, you’ve been deeply involved with the development of glTF, the Khronos standard for models and scenes. How did you first get involved in open standards?

Don: I happened to be personally interested in building my own projects with WebGL around the time draft versions of glTF 2.0 were coming together. Loading 3D models into the scene correctly was a real challenge—existing loaders weren’t enough if the format itself wasn’t designed for runtime transmission or isn’t carefully documented in a technical specification.

The vision for glTF immediately felt right—runtime transmission, detailed specifications, and a scope that was opinionated and focused enough for complete implementation and specification to be possible.  I started contributing to a glTF loader in three.js and was introduced to Patrick Cozzi and others at the Khronos Group soon after that.

After that, finding more ways to get involved was easy: there are always more interesting technical challenges than people to solve them. I was also very fortunate to be working with a team that allowed me to spend a percentage of my time on self-directed work in open standards and open source.

Since then I’ve written the glTF Transform library, which is popular for optimizing existing 3D models, but at the same time it’s a very flexible framework for creating or modifying glTF models, or managing custom glTF extensions. I’ve also written three-ish glTF loaders now (too many?)  and a couple popular viewers like gltf.report/.

Amanda: Sean, you’ve been a key contributor to 3D Tiles since its inception. 3D Tiles is an OGC community standard for streaming massive 3D datasets, and is built on glTF. What drew you into the open standards space?

Sean: I first got involved in open standards when I joined Cesium in 2015. Previously, I was using COLLADA and OpenGL in a personal game engine project and was already a big fan of Khronos. One of the first projects I worked on at Cesium was obj2gltf, which started during a code sprint in the Poconos, and later gltf-pipeline.

This was also the year 3D Tiles was announced; I contributed to the specification, CesiumJS implementation, tiling pipelines, and was quite active on the Cesium Community Forum.

Amanda: Both 3D Tiles and glTF have revolutionized the way people visualize 3D data, but that’s just the beginning. I know we have some key work going on in 3D Formats right now with a new glTF version on the horizon and a new 3D Tiles coming right behind it. How do you see these standards evolving over time?

Don: glTF has been successful over the years, at least in part because of its unique focus on efficient, last-mile transmission to runtime. The line glTF needs to walk as it evolves, I think, is to keep that focus while understanding that the mission is a moving target, and that capabilities of runtimes and last-mile 3D data are also evolving.

Other open source or standards projects like OpenPBR, MaterialX, and USD are worth mentioning here. While they don’t necessarily share that transmission-to-runtime goal, they absolutely represent an evolution (for the better!) in 3D content creation, and these changes feed into workflows around glTF.

Importantly, glTF today provides the “building block” for extension into very different use cases – 3D Tiles and VRM especially. I hope that doesn’t change; it’s an important balance of scope.

Sean: At the same time, the community might benefit from glTF and 3D Tiles converging over time. In 3D Tiles 1.0 we had the Batched 3D Model and Instanced 3D Model formats that wrapped binary glTF. In 3D Tiles 1.1 we saw these capabilities move into glTF extensions that allowed 3D Tiles to reference glTF directly.

And now, in the other direction, there's an industry wide push towards using glTF for complex scenes; for example, the AEC industry using glTF for massive design models, and e-commerce using glTF for level of detail.

It seems to me that 3D Tiles and glTF are meeting somewhere in the middle, while staying true to efficient transmission.

Amanda: What community projects using glTF and 3D Tiles are you keeping an eye on?

Don: I worked with R&D at The New York Times a few years back, and they’ve done some really excellent work using both glTF and 3D Tiles in different projects, such as visualizing the progress of the fires in Maui in 2023. They’ve also written “field guides” sharing their processes and learnings for publishing 3D content in journalism.

Sean: Ever since the Google Maps Platform released their worldwide dataset as 3D Tiles, members of the larger community have been building all sorts of interesting applications with that data, like visualizing building projects in context or showing stadium locations in sports reels.

I'm really looking forward to Cesium Native getting WebAssembly support so that we can bring Cesium Native's 3D Tiles streaming engine to the browser.

I'm also actively following Garrett Johnson's 3D Tiles Renderer for Three.js.

Amanda: It’s clear both of you have contributed significantly to the tools and standards making 3D graphics easier than ever to share. What does it mean for Bentley to bring this kind of talent together?

Sean: It’s exciting. Don’s work has influenced how developers and artists optimize and publish 3D content. His tools like glTF Transform and gltf.report are widely used. Having him on board means we’re doubling down on our commitment to open standards and high-quality tooling.

Don: I’ve collaborated with the team before, including on 3D Tiles 1.1. Joining Bentley now feels like a natural next step: Bentley’s investment in open standards is a big reason I’m here. It’s rare to find a company that not only uses open formats but invests in helping define them.

Amanda: For readers interested in pushing the forefront of open standards, how would you recommend getting involved?

Sean: The Cesium community forum is very active and a great place to help other people building in 3D. And the 3D Tiles repo on GitHub is a great place to share ideas.

Don: There’s always need for people to pitch in. If you’re passionate about open standards, the Khronos Group is always looking for volunteers interested in supporting the future of graphics. And the Metaverse Standards Forum, as you know, is doing some really interesting interdisciplinary work.

Amanda: We’re deeply committed to building the tools for an open ecosystem. If you’d like to join us, check out our current openings.