How the iPhone and iPod Touch are location aware

Being inside a Conrad store in Germany just makes you buy stuff you normally might not. I was in the Hannover branch last Sunday, on the tail of a CeBIT visit, and bought an iPod Touch. And I’m about as close to being in love as you can be with a non-human subject.The iPod Touch got a (paid) software upgrade in January, and now all of a sudden it has a Maps application, and what’s more: Maps has a location button that invokes some magic to determine your location. Without GPS. This magic is courtesy of Skyhook Wireless and uses the broadcast signals of WiFi access points to triangulate your location. It’s called WPS, WiFi Positioning System.This video is a very good high level introduction to the technology. Skyhook has an introductory page about the technology as well Let me summarize the key pluses and minuses.

  • Unlike GPS, WPS functions well indoors and in densely built up areas.
  • Location is determined extremely fast when compared to GPS, typically in <1sec.
  • No extra hardware is needed, a 802.11 network interface and antenna suffice.
  • Reliance on WiFi access points means no WiFi, no location: rural areas and water bodies are out.
  • Service coverage is dependent on Skyhook expansion policy: they decide what’s good for us.
  • There’s no two-way communication to help Skyhook improve the database.

The coverage of the service is by its nature limited to urban areas. The mapplet on this page shows the current coverage visually. Coverage in the Netherlands is limited to Amsterdam and part of Rotterdam. For Western Europe in general, you could say that the larger built up areas are covered. Skyhook:

WPS currently provides coverage to 70% of the American, Canadian, and Australian populations. By the end of March 2008, Skyhook will have coverage in the top 50 metropolitan areas of Europe as well as cities and towns representing 50% of the UK, French and German markets.  

Skyhook can and will work with partners and customers to add new coverage areas, or to accelerate expansion into planned areas, in support of mutual commercial opportunities.

Well, that’s all marketing bla-bla – what they really should do is open up their database for user submissions. Sure, you can submit an individual access point through the Skyhook web site, but that’s a far cry from an automated harvesting application. All the basic ingredients are there: The iPhone SDK, the Skyhook SDK, and a large user base. A quick look at the Skyhook SDK tells me it’s just about getting a location; I see no functions to submit any kind of feedback – harvesting results – to Skyhook.All in all it’s a start, and part of me is happy to be done with the sub-par performance of GPS in built-up areas. A slightly bigger part of me longs for a solution based on open, user generated content. For the iPhone, the Antenneregister – a government-maintained registry of all GSM and UMTS cell towers in the Netherlands – is promising. afbeelding-194.pngThe database is right there on their web site: more than 23.000 geocoded cell towers. The only thing that’s missing is ther cellID… Automated harvesting of cell tower data is nothing new either, here’s an implementation called IYOUIT that harvests for a worldwide cell tower database (Google Earth network link) initiated by the Telematica Institute. Further reading aplenty.


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