Is this based on 3D model or just 360 photo? I looked at the online demo, it doesn't appear to be 3D model. But if it is based on 360 photos, how does it perform the transition between different viewing locations? Streetmap, for example, can't do very smooth transition.
This would make sense as it's based on Google Earth which is 3D.
Even WebGL web version of Google Maps is already 3D since some time ago. See e.g. Colosseum here:
https://www.google.com/maps/place/Colosseum/@41.8950247,12.4...