In general, you can use 3D Tiles terrain data from a local machine. Some details are given at Adding Datasets – Cesium , but you actually already did it correctly, by setting the Source to be a URL that points to the local file.
The reasons for the the two tilesets not being displayed are different ones:
For the TilesetWithTreeBillboards, it will print a message (in the output log that can be shown with “Window → Developer Tools → Output Log”), saying
No loader registered for tile with content type ‘’ and magic value ‘i3dm’.
This just means that the tileset uses Instanced 3D Models (I3DM), which are not yet supported by Cesium For Unreal, but will probably be supported in a future version.
For the “Temporal Lyon” data set that you linked to, it’s … a bit more complicated. The data set has some issues. For example, it declares strange transforms and bounding volumes, like
“transform”: [1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 1841958.443, 5175950.416, 194.769, 1.0]
When “fixing” these pragmatically (with a text editor), it does display something, but the result is likely not the intended one: The data set uses an extension that is called 3DTILES_temporal. I don’t know any details about this extension, but it is not supported by Cesium For Unreal (and probably not by CesiumJS either - it seems to be a proprietary one, mentioned in [3D Tiles] What is tileIndex ? · Issue #1039 · iTowns/itowns · GitHub , but not available under the given link…). On top of that, the glTF data that is contained in the B3DM has 14 validation errors (but these are only related to the accessor bounds - so the glTF is invalid, but could still be rendered by Cesium For Unreal).
So in general, if you have a (valid) terrain data set that uses the most common content type (namely, B3DM or composite tiles), you should be able to display it with Cesium For Unreal by just setting the URL as you did it. But when the data set is invalid or uses features that are not supported yet, you may encounter different issues that would have to be sorted out on a by-case basis.