On Tuesday 29 June 2010 14:09:47 Sam Smith wrote: > On Tue, 29 Jun 2010, Tom Steinberg wrote: > > In fact, here's an idea. A voluntarily installed mobile app that only > > shares your location data when you appear to have taken some sort of > > public transport along a known route, between known nodes. > > > > Just a leeetle bit tricksy > > geotagged tweets and a hashtag? >
Hey, I was looking for an excuse for a first Android app. I can see many significant problems with trying to auto-detect the state of being on public transport. First of all, there's the "High geographical entropy" approach - have you suddenly moved a lot? if so, where were the start and end points? geocode'em, do a bounding box search against a db of bus stops, record the route and time taken. Unfortunately, this relies on somehow sensing which form of transport was used, and the problem there is that in town, speed won't do as traffic is often at walking or cycling pace. Second problem - it also involves a background service checking GPS locations, which on Android is a sure fire battery killer. Third problem - anybody got a database of bus stops? Another problem would be ambiguous stops - a lot of bus stops and tube lines and railway stations are the same place or at least within typical GPS circular error probable (and doesn't that phrase take you baaack to the cold war). Obviously, being prompted as to whether you were about to take a bus every time you were within 24 metres of a bus stop would be tiresome. At the moment I can't think of any other heuristic; I suppose if you were using a pay-by-phone application (Arriva does this in some places) you could detect it or even snarf the data. So I think user-declared data is probably the way to go. Tweets are one option, an SMS shortcode is another (although, in some ways twitter-by-SMS replicates a lot of the functionality). Hmm, what about the Oyster account web interface? There can be no objection to screenscraping your own account. Of course that creates a systematic bias towards postpaid Oyster users which may or may not be significant. Alternatively, at least for London, we could wait for TFL to release its bus data API and then just pull that in:-) -- The only thing worse than e-mail disclaimers...is people who send e-mail to lists complaining about them
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