There's a lot you can do with just a single camera and imu. PTAM is just one example there are other formulations but it tends to work well without using a ton of CPU/GPU resources
There are a few things stacked on top of each other to make it happen, but this is a good start.
Combine this with GPS information and you can roughly "place it in the world" and make sure it doesn't clip the ground plane. After that, it is just pulling it up from your sparse 2D DB and dumping into the scene for other cameras. If they really care, there'll be some data included from the placement camera to help localize it.
PTAM has been around for a while. There's newer techniques for monocular slam, but I've not heard of any that were "consumer ready". Any ideas on whether they are using a new semi-dense approach or improving an existing paper?
Combine this with GPS information and you can roughly "place it in the world" and make sure it doesn't clip the ground plane. After that, it is just pulling it up from your sparse 2D DB and dumping into the scene for other cameras. If they really care, there'll be some data included from the placement camera to help localize it.