On Tuesday 29 June 2010 19:06:32 'Dragon' Dave McKee wrote: > > [Autodetect location] > > 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. > > If we assume they're not cycling
Why? I would think cyclists are more likely to be public transport riders than the genpop. > (or driving, for that matter) for > now, they shouldn't be going much faster than 15 mph* over any > sustained distance, or 20 mph** instantaneously. If we see those, we > assume they're in a bus or similar. (I assume the GPS will > successfully work in a bus in the same way a car's does?) > *: fastest marathon average speed > **: an 11-second hundred metres. > We may be able to rule out cycling and cars if they continue at a high > speed which doesn't tally with a known route, or don't have near-zero > velocity at a valid start/end point. We could also use whether the bus > regularly stops (and potentially use that data, too.) > We may. It's certain, however, to be a hell of a lot of work, and to involve a lot of testing to get the false positive rates down. > > Second problem - it also involves a background service checking GPS > > locations, which on Android is a sure fire battery killer. > > This is a major hurdle. > Yes. All "guess that this person has been on the tube" approaches hit this, because they all involve a background service checking GPS. In fact, my own experience of Android is that it's not so much GPS. Any background service is a killer. You could happily run the Symbian Skype app, even though it uses the radio network, without pulling standby time under a working day. Not so much for really anything in 'droid, and iPhone OS doesn't even let you multitask. I know an N900 user and will quiz him. > > Third problem - anybody got a database of bus stops? > > Already answered. > > > 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). > > We might not be able to differentiate between stops, but we can > differentiate between lines. Unless, of course, the bus line follows > the tram line for the whole journey (not unreasonable.) We can always > ask when we ask the user to confirm that a journey has occurred. > > > 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. > > You don't need to prompt until they get off, perhaps? > Yes. You need to prompt for where they began the journey. Otherwise a permanent location logging service is required, reducing standby time to half a working day. Beyond battery, it's just inelegant to log EVERYTHING and try to work out what is relevant. It's also against our principles. We're not in this business to collect everyone's movements and let them trust that we throw 'em away.. > > 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). > > Users remembering to submit data is likely to have a significant > sampling bias: 'oh, the bus was really slow yesterday, I should > measure it today.' > I think this is a deep conceptual issue. If we insist that there must be no user intervention, we have to come up with some berserk heuristic tree for guessing if you're on a bus, we have to insist on battery guzzling background ops that won't work on iPhone OS, etc etc. But if somebody's installed this app, they are by definition committed to the project. Why else install it? We could push it out to DemocracyClub volunteers...eh, what happened to that... > > 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. [also, pay by phone] > > This is probably less bias than 'has a GPS-sensing phone and got the > app' will introduce. > > No, I suspect it may be the best option. Even if MySoc people don't have Oyster accounts, following the lead of Chris Lightfoot, it's less pomclipacated than bus-guessing. > _______________________________________________ > Mailing list [email protected] > Archive, settings, or unsubscribe: > https://secure.mysociety.org/admin/lists/mailman/listinfo/developers-public > -- The only thing worse than e-mail disclaimers...is people who send e-mail to lists complaining about them
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