Introducing GEO_LOD: a vendor extension for per-part LOD switching in glTF

ascotsman4evr · June 24, 2025, 1:44am

Hi everyone!

I’ve just opened a PR to add a small Vendor extension called GEO_LOD to the glTF registry:

github.com/KhronosGroup/glTF

Add GEO_LOD vendor extension for per-part LOD

main ← andybushnell:add-geo-lod-extension

opened 01:20AM - 24 Jun 25 UTC

andybushnell

+88 -0

In visual-simulation toolchains (e.g. OpenFlight/Aechelon/Geo STUDIO), it’s rout…ine to define per-part LOD variants directly in the model hierarchy. You might have a tank’s chassis split into high/med/low meshes under one grouping node, its turret under another, its wheels under yet another—all within a single file. No “root-only” swapping, and no need to carve your model into separate glTFs for each LOD. By contrast, glTF’s built-in LOD patterns (e.g. MSFT_lod) expect a single node that is the LOD switcher, listing mesh indices. That works, but it can’t express “here’s a chassis, with three mesh children,” or “here’s a turret behavior, with its own LOD children,” in one neat file. Enter GEO_LOD—a small vendor extension that you attach to any grouping node (having no mesh of its own) whose children (the entire sub-tree parented by the LOD node) are considered the LOD variant for that part. Your loader/runtime software then simply activates that LOD node (and its children) based on it passing the distance or screen-coverage switchin & switchout criteria. Any dynamic transformation applied above the LOD in the hierarchy will automatically be applied to the active LOD.

This lets you tag any grouping node (mesh-free) with [switchIn, switchOut] thresholds by distance or screen coverage, and your loader will only traverse and render the active subtree.

All the details (JSON Schema, README, and two live example models) are bundled in that PR under extensions/2.0/Vendor/GEO_LOD. Any feedback on the schema or spec would be hugely appreciated!

– Andy Bushnell

PS i’m a total newbie to github, so apologies if things are rough around the edges!