You could do every 5 minutes - but that would still be impossible on the iPhone, where your phone would have to remain unlocked (i.e. screen on) and your app open the entire time to do so. That is perhaps a bigger battery hog than the GPS receiver itself.
Also bear in mind that position acquisition is far from instantaneous, and has a high fixed cost. 5 minutes is probably ok, but keep in mind that your receiver is puttering away for a good minute before your scheduled check-in, just so your GPS can reacquire its position.
This would work if the software was integrated into a GPS unit, but not a cell phone. Taxi drivers in particular always have their GPS units chained to a car charger source, and this eliminates your power issue. Further, a GPS unit doesn't need to be hacked to support background applications :)
I think you misunderstand the intent of the idea - which is to use other people stuck in traffic jams to warn others who are approaching to divert. This absolutely requires a GPS unit of some sort. The data in this model is emergent, as opposed to human processed (e.g. a driver calling in an accident at an intersection).
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You could do every 5 minutes - but that would still be impossible on the iPhone, where your phone would have to remain unlocked (i.e. screen on) and your app open the entire time to do so. That is perhaps a bigger battery hog than the GPS receiver itself.
Also bear in mind that position acquisition is far from instantaneous, and has a high fixed cost. 5 minutes is probably ok, but keep in mind that your receiver is puttering away for a good minute before your scheduled check-in, just so your GPS can reacquire its position.
This would work if the software was integrated into a GPS unit, but not a cell phone. Taxi drivers in particular always have their GPS units chained to a car charger source, and this eliminates your power issue. Further, a GPS unit doesn't need to be hacked to support background applications :)
I think you misunderstand the intent of the idea - which is to use other people stuck in traffic jams to warn others who are approaching to divert. This absolutely requires a GPS unit of some sort. The data in this model is emergent, as opposed to human processed (e.g. a driver calling in an accident at an intersection).