October 28, 2008

The really revolutionary thing about the iPhone’s GPS system (‘A-GPS’, or Assisted GPS) is that it nearly always has a fallback option. First it tries to get a fix on a GPS satellite; if it can’t do that, it tries to locate you via wifi (hopefully more accurately than whatismyipaddress.com, which thinks I’m in Solihull, or ip-adress.com [sic] which thinks I’m in London — both quite wrong). If wifi fails, it tries to triangulate your position from mobile phone towers. I guess the reasoning is that if you’re out of reach of satellites, wifi and phone reception then really, you’re completely lost in more way than one.

homing in

Google maps: homing in

The iPhone has a similar strategy when it comes to internet access: if there are local known wireless networks available, it will try to join them; if there are local unknown wireless networks available, it can be configured either to prompt you to join them or let you find them for yourself. If wireless networks can’t be found or joined it will try for 3G; if that fails, EDGE; if that fails, GPRS.

iPhone networking symbols

iPhone networking symbols

Try for the best first; but be prepared to accept second best, third best, and so on, to the bitter end. It’s the same strategy as Emily Dickinson describes:

The Heart asks Pleasure — first —
And then — Excuse from Pain —
And then — those little Anodynes
That deaden suffering —

And then — to go to sleep —
And then — if it should be
The will of its Inquisitor
The privilege to die —