Using WiFi to triangulate instead of GPS

I know its probably possible, but is it practical and doable to try and geo-position someone using WiFi to triangulate...

Thinking if I was underground and didn't have access to GPS, could I setup WiFi spots around the place to help locate someone.

Or if I was on a plane or a train (which is constantly moving), could I setup WiFi spots around the place to help locate someone.

Where would I start in doing this? Is there software components/infrastructure? If not would it be possible to do this... i.e. at a router level add location information to the packets about which router the incoming message was coming from and then the server being able to pick up on this... 开发者_StackOverflow社区

This is exactly how the Skyhook database (built into many phones) works. It uses cell towers and WiFi points to triangulate the position in the absence of a GPS signal.

Google also does this with their street view vans—they look for open wi-fi networks as they go, and record their positions.

This is already widely available. Google the terms wifi location aware.

This is how laptop "Lo Jack" theft recovery systems work, for example.