{"action":"created","issue":{"url":"https://api.github.com/repos/graphhopper/map-matching/issues/86","repository_url":"https://api.github.com/repos/graphhopper/map-matching","labels_url":"https://api.github.com/repos/graphhopper/map-matching/issues/86/labels{/name}","comments_url":"https://api.github.com/repos/graphhopper/map-matching/issues/86/comments","events_url":"https://api.github.com/repos/graphhopper/map-matching/issues/86/events","html_url":"https://github.com/graphhopper/map-matching/issues/86","id":194421695,"number":86,"title":"suboptimal (?) transition probability metric","user":{"login":"kodonnell","id":8204904,"avatar_url":"https://avatars.githubusercontent.com/u/8204904?v=3","gravatar_id":"","url":"https://api.github.com/users/kodonnell","html_url":"https://github.com/kodonnell","followers_url":"https://api.github.com/users/kodonnell/followers","following_url":"https://api.github.com/users/kodonnell/following{/other_user}","gists_url":"https://api.github.com/users/kodonnell/gists{/gist_id}","starred_url":"https://api.github.com/users/kodonnell/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/kodonnell/subscriptions","organizations_url":"https://api.github.com/users/kodonnell/orgs","repos_url":"https://api.github.com/users/kodonnell/repos","events_url":"https://api.github.com/users/kodonnell/events{/privacy}","received_events_url":"https://api.github.com/users/kodonnell/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":6,"created_at":"2016-12-08T19:23:34Z","updated_at":"2016-12-12T12:55:18Z","closed_at":null,"body":"Currently, our transition probability is higher for transitions which are close to a straight line. I see a few problems with this:\r\n\r\n- it's possible that the the wrong transition is favoured. E.g. say I have a candidate which is 100m away, but in exactly a straight line. If I have another candidate which is only 10m away, but slightly off a straight line, then the former will actually be favoured.\r\n- shouldn't we be using time, not distance (or at least allow the user to configure this)? The transition probability is meant to indicate the likelihood of transitioning (funnily enough) from one candidate to the next - and personally I think that most people think in times not distances. E.g. if I have two routes and one if 5 minutes faster than another, I'm more likely to take that, regardless of the length of either route. Put another way, changing to time-based transitions would mean that e.g. travelling along highways is more favoured than side roads. Again, we should easily be able to configure this.\r\n- I'm not sure we need to scale by the square of the time difference - if this scales all of the probabilities by the same factor, then won't this leave the final viterbi sequence unchanged? We'd probably remove this if we did time-based transitions anyway ...\r\n\r\nThat all said, I suspect most of these will only have noticeable differences when routing over larger distances (e.g. hundreds of meters).\r\n\r\nThoughts @stefanholder ?"},"comment":{"url":"https://api.github.com/repos/graphhopper/map-matching/issues/comments/266424408","html_url":"https://github.com/graphhopper/map-matching/issues/86#issuecomment-266424408","issue_url":"https://api.github.com/repos/graphhopper/map-matching/issues/86","id":266424408,"user":{"login":"michaz","id":520916,"avatar_url":"https://avatars.githubusercontent.com/u/520916?v=3","gravatar_id":"","url":"https://api.github.com/users/michaz","html_url":"https://github.com/michaz","followers_url":"https://api.github.com/users/michaz/followers","following_url":"https://api.github.com/users/michaz/following{/other_user}","gists_url":"https://api.github.com/users/michaz/gists{/gist_id}","starred_url":"https://api.github.com/users/michaz/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/michaz/subscriptions","organizations_url":"https://api.github.com/users/michaz/orgs","repos_url":"https://api.github.com/users/michaz/repos","events_url":"https://api.github.com/users/michaz/events{/privacy}","received_events_url":"https://api.github.com/users/michaz/received_events","type":"User","site_admin":false},"created_at":"2016-12-12T12:55:18Z","updated_at":"2016-12-12T12:55:18Z","body":"I just wouldn't think of it as \"turns are unlikely\", but as \"turn instructions in the result must pay rent in increased accuracy.\""}}
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