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Faster 3D Models with Binary glTF

Patrick Cozzi

Update: This initial work on Binary glTF has led to the KHR_binary_glTF extension, which should be used instead of CESIUM_binary_glTF.

Starting with Cesium 1.10, the new Binary glTF extension makes 3D models 10-30% faster to load, especially models with a lot of geometry. To use it, select the Binary glTF option in the Cesium model converter, which will return a .bgltf file that can be loaded with Cesium 1.10 or later using the same API as usual.

Read on for the under-the-hood details.

glTF is a JSON format with binary payloads for geometry, textures, animation key frames, and skin inverse-bind matrices. These resources are referenced by uri using a glTF buffer, so they could be separate from the JSON:

"buffers": {
    "duck": {
        "byteLength": 102040,
        "type": "arraybuffer",
        "uri": "duck.bin"
    }
}

or embedded using a data uri:

"buffers": {
    "Cesium_Air": {
        "byteLength": 172256,
        "type": "arraybuffer",
        "uri": "data:application/octet-stream;base64,AAAAAMGqKj6fqq..."
    }
}```

Previously, the Cesium model converter base64-encoded external resources for simplicity.

Cesium 1.10 introduces support for Binary glTF (CESIUM_binary_glTF), a glTF extension that defines a binary container format containing the glTF JSON and binary resources (and shader sources).

Binary glTF layout.

Binary glTF has the convenience of a single file, like using data uris, but is smaller since binary data is not base64-encoded, and faster to load since base64-decoding is not required at runtime.