Hi @pavlo
To answer your first two questions, the 3D Model → 3D Tiles pipeline doesn’t currently preserve per-feature information, whether it’s coming from EXT_mesh_features / EXT_structural_metadata or from glTF nodes. It’s a common feature request and one of the things we hope to look at after we launch the new photogrammetry pipeline.
Those are still valid bug reports though: the extension should not be included in extensionUsed and the second model should not crash.
For your third question, see these related issues:
- 3D Tiles Next Metadata Compatibility Matrix · Issue #10480 · CesiumGS/cesium · GitHub
- `Model` EXT_mesh_features: handle feature IDs without a property table · Issue #9884 · CesiumGS/cesium · GitHub
The crux of the issue is that since feature ids can be arbitrary values (including very large values) we aren’t able to pre-allocate ModelFeature objects like normally do when a property table and count are known. The workaround is to add the EXT_structural_metadata extension with an empty property table (a count, but no properties).
I’ll mention this post in the second issue just see we can keep track of this.
Thanks!