[OSM-talk] Detecting unwanted edits and vandalism

Paul Norman penorman at mac.com
Sun Apr 8 22:34:26 BST 2012


> -----Original Message-----
> From: Dmitry Terentiev [mailto:Djterentjev at yandex.ru]
> Sent: Sunday, April 08, 2012 12:16 PM
> To: talk at openstreetmap.org
> Subject: Re: [OSM-talk] Detecting unwanted edits and vandalism
> 
> Adam,
> Very often newbie to OSM start their contribution with moving object
> according misaligned imagery.They just don't know imagery can be offset.
> It's can be detected automatically. Plus overleaping or unconnected
> ways, ways without tags, intersections without shared nodes.
> 
> It will be grate If we can have such a tool to analyze changesets.

Some technical thoughts on detecting these:

If you compute the displacement of each point moved a mass move should show
up as a low standard deviation/1st moment of area.

Alternately, if you normalize the moments of area right a move of many nodes
all in the same way should all be equal.

The problem with this is that determining the distance moved requires a
/history API call and full history dumps are difficult to work with.

Ways without tags should be easy to detect - every untagged way created
should be added to a relation in the same changeset. Tags being removed from
a way with no relation membership added in the changeset is not necessarily
an error, it could already be a member of one.

Intersections without shared nodes is difficult. If working on current
changesets it doesn't require any history calls but it requires issuing a
map call for each node you want to check. Or you could run it with direct
access to a database and use a database query. Either way, the problem is
that every node created needs checking.




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