[OSM-talk] (magical?) road detector

Thibault North tnorth at fedoraproject.org
Sat Feb 5 16:22:11 GMT 2011


Hi Ido, 

Could we have more information about how the road detector works?
I gave it a quick try, and wrote a few thoughts about it after making a short 
comparison with the use of Dijkstra's algorithm.
See http://tnorth.ch/blog/index.php?post/2011/02/04/Bing-road-detect-API-and-
vectorization

Thanks,
Thibault

> On Fri, 2/4/11, Ido Omer <Ido.Omer at microsoft.com> wrote:
> 
> From: Ido Omer <Ido.Omer at microsoft.com>
> Subject: [OSM-talk] (magical?) road detector
> To: "talk at openstreetmap.org" <talk at openstreetmap.org>
> Date: Friday, February 4, 2011, 7:59 PM
> 
> Hi Guys,
>   
> I am a researcher at Microsoft and I am currently working on the road
> detector. I joined a bit late and can’t post answers in the existing road
> detector thread, but I might be able to provide some additional info
> regarding the road detector. It is *FAR* from being perfect, but in our
> experiments it may produce a lot of value (== save time) if you use it
> correctly. When use it correctly means don’t expect too much, so here are
> some practical tips: 1.
> It is currently uses the two end points as example and tries to find a path
> that is similar to those examples, so it is recommended to use the tool at
> a zoom level that will let you make sure you click on a road and not near
> a road (we will probably loosen that restriction in the future). 2.
> Don’t try to challenge the detector too much, it will probably fail,
> instead if you have a very complicated winding road break it into a few
> sections and let it detect shorter legs (it will still save you most of
> the clicks…)
> 3.      
> One of the main features used is color, so if the road changes its color a
> lot, break it again into shorter legs. 4.
> We currently only compute one path (road) between the points and cannot
> provide a meaningful score for that path. Defining a score is a difficult
> problem (but we are open to ideas…). 5.
> To speed things up, we are using a bounding box that is in many cases
> smaller than the bounding box provided by the client (we take constant
> margins around the bounding box defined by the two end points). This means
> that if you click on the two end points of a U shaped road we might
> truncate the lower part of the U and find a “shortcut “ through buildings,
> fields, etc. And again you’ll need to break the query into shorter legs…
> (I am currently working on speeding things up and I hope to get rid of
> this limitation in a week)
> 6.      
> The algorithm is currently ignoring junctions, but I should be able to add
> them very soon (early next week) That is for road detection. The other
> mode we will provide is road exploration which will enable finding all the
> roads in a certain bounding box (well, you’ll probably need to click once
> or twice…) I am not sure if there is an exposed version of this service (I
> hope not, since so far it is really a bunch of experiments…) but we should
> have it really soon (a week or two). For the road exploration we will
> probably have some kind of certainty level for each road segment. 
> I will be very happy to hear of any complaints/requests/places where you
> think the detector should work but it fails/any other feedback. 
> Thanks,
> Ido
>   
> 
> 
> 
> 
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