I just learned about cesium.com/ion. It is a website that allows one to create ‘Assets,’ or sets of 3d-tiles, and host them for a cesiumjs.org instance such as webglearth.com ( 3d Leaflet ) . One can choose to upload (3d aerial photogrammetry)[https://cesium.com/docs/tutorials/uploading/] that gets carved into vector 3d tiles that are hosted as an Asset through Cesium. Each tile is one WebGL draw call.

Somebody might want to grow these 3d-tiles from the ground up artificially if he can’t fly from the skies. An Asset producer may regularly update from OSM in order to parse the tags for elevation, vegetation, buildings, etc in order to grow the tiles based on tags.

Some fun with Assets: let’s say you had 3 ‘visibility layers’ to choose from, those being buildings, vegetation, and terrain. To maximize efficiency, you should host X Assets if you have Y visibility options: X := Σ for n=1..Y, Y choose n. Basically, one Asset for every possible selection.