The principle behind GPS technology is relatively simple, you have a network of satellites where their location is known to a high degree of accuracy, and you have a way to determine the distance between that transmitting satelite and the receiver. You need a minimum of 3 satellites to triangulate a location, and obviously the more you fix on, the better your accuracy. A company called Locata has a similar ground-based system that works on the same frequency as Wi-Fi and can be used to get location accuracy on the order of 1-cm! The military has been using it to track munitions on a missile range, but the technology is now being rolled out for civilian applications. I could see this being really useful on construction sites, in underground mines and perhaps for structural monitoring applications and probably more things. The units have a range of several kilometers. [Source: Slashgeo.org. Image: Technology Review]
