How should i sync my 3D point cloud with cesium world?


I’m very new to cesiumjs.

Thank you in advance for any help.

I have locations and building witch is partially on ground and partially underwound.

I want to use a drone and collect building point cloud data after that i wat to visualize that in cesiumjs.

How do i align it with cesium map ground and the rest of building should show underground.

Also another thing i would like to show drone flight trajectory.

I have point cloud and trajectory data now, but once i load point cloud tiles in cesium js and i add trajectory to the map everything is out of sync and not even near what i try to achieve.

Any suggestions welcome. Really need help here.