How does Threejs integrate with the map?

Threejs is really easy to learn, but how to use it in webgis projects

How to import the 3D model?

Is it loaded in threejs? Or is it loaded in the map?

https://so.csdn.net/so/search?q=threejs%20gis&t=&u=

threegeo

threejs mapcontrol:https://threejs.org/examples/misc_controls_map.html

threejs combined with mapboxgl? Or the combination of threejs and baidujs? Or is it combined with Gaodejs? threejs combined with cesiumjs

How threejs performs coordinate system conversion. How to define the coordinate system first