Is it possible to make cesium-like tool with Unity ? but offline.

Hello everyone ,

I'm trying to create a Unity game which will run on a private network (Offline/No-Internet connection). There will be terrain data (Most-common GIS formats can be used) and buildings data(BIM, kml etc. something similar to OSM) being streamed from a custom server. So, I have been trying to find the best approach for a while and wanted to see if there's something different that this community can offer..

Is there anything that you guys can show/ refer to ? -If there is any- What's the best tool for doing that ?

Thanks in advance !

Basically : Something like Cesium for Unreal would do it.