During the last six months or so I've been actively engaged in researching and looking into real, sustainable alternatives to GPS for indoor location, as we all know GPS don't work indoors.
With the advent of both iOS and Android devices supporting the Bluetooth 4 protocol and in particular the Bluetooth Low Energy (BLE) element of that protocol, there has been a plethora of companies set up to exploit the iBeacon system. I'm currently playing around with a set up that utilises both wifi and BLE to map your location and eventually give directions.
But these "smart phones and devices" are continually being given hardware upgrades by the likes of the board manufacturers. Some like the iPhone/iPad have had them for some time but it is only now that they are being exploited as uses and software are being found for them.
Apparently awhile ago a Finnish student undertaking a PhD thesis was exploring the earth's magnetic field. Somehow from this research he found the building threw up magnetic anomalies which in turn by using some code he could measure. This could be mapped and hence be used as a location.
You to can now play with this development code if you have an idevice that supports Bluetooth 4.
https://www.indooratlas.com/ From a mine exploration view in their FAQs the following appears:-
Is IndoorAtlas working in underground environments?
?IndoorAtlas may work in an underground environment if the environment contains enough magnetic information. We have successfully tested the IndoorAtlas’ technology in underground mining tunnels (1400 m below the surface), where the metal ore is contributing to the magnetic anomalies.
So there you go the possibility of underground route finding out of GPS reach..........maybe.
Peter.
Extra link, CEO talks about it[youtube]4LzSs3_dL7w[/youtube]