classificationType

Gets the model's classification type. This determines whether terrain, 3D Tiles, or both will be classified by this model.

Additionally, there are a few requirements/limitations:

The glTF cannot contain morph targets, skins, or animations.
The glTF cannot contain the EXT_mesh_gpu_instancing extension.
Only meshes with TRIANGLES can be used to classify other assets.
The meshes must be watertight.
The POSITION attribute is required.
If feature IDs and an index buffer are both present, all indices with the same feature id must occupy contiguous sections of the index buffer.
If feature IDs are present without an index buffer, all positions with the same feature id must occupy contiguous sections of the position buffer.

The 3D Tiles or terrain receiving the classification must be opaque.