Underground positioning

Yesterday, I was in the subway and like many people, I need to keep myself busy during my commute. So I started playing with my phone and when I started Navizon, I noticed that the phone light was green. Even though there is not enough signal to make a phone call, I figured that Navizon might receive a tiny signal from an outside cell tower, enough to get a position fix.

So the next day I switched Navizon to "local mode" (in order not to require an Internet connection to get my position), synchronized my data and took the subway again. And... bingo!! I was able to get my position during my entire commute. Pretty cool especially since there is no other alternative method to get your position when you are underground: Navizon can be an alternative to GPS when you are outside but in an underground environment, there is no way GPS will work, so it might very well be the only working solution.

So what do you need to reproduce the experiment?
- an HTC smartphone: I am using an imate SP5m but there are other devices that would do the trick like the T-Mobile Dash
- the latest ROM update for your phone: it started working only after I installed the latest ROM update for my phone as it looks like it makes the cellular reception a little better
- Navizon running in local mode, with the data for your home area synchronized on your device.

Why an HTC smartphone? Simply because on these phones, Navizon can triangulate signals from many cell towers. And it looks like it is able to still receive a little bit of signal in an underground environment.

So I don't if this thing can be useful to someone, but I figured that first responders or underground municipal workers might like the idea. There is also this app that I have had in the back of my mind for quite a while: I always thought it would be cool to have the traffic map for the subway, just like you have  for standard traffic. With this app, one would be able to know when the subway system is congestioned, and probably be able to save the precious half hour waiting for the train during rush hour.