[OSM-newbies] OS_OpenData

[SomeoneElse]

Dudley Ibbett wrote:
> I wonder if anyone that has had experience of using 
> OS_OpenData_Streetview in the UK could comment on its accuracy.  I 
> have been doing some mapping through Earl Sterndale in Derbyshire and 
> note that most of the buildings are drawn with the source tag: 
> OS_OpenData_Streetview.  Many of the buildings positions and shape are 
> way off compared to Bing.  Should I consider adjusting them according 
> to Bing or leave them alone?

Generally speaking, in an area that's flat and not hilly, I'd expect 
OS_OpenData_Streetview to be within 2-3m of an average of lots of GPS 
traces.  There's the occasional anomaly, where roads come out the wrong 
shape or features are misinterpreted (presumably as a result of tracing 
from aerial photos), but it's usually there or thereabouts.

My gut feeling for the Bing imagery in similar conditions is that 
usually it'll be more accurate than OSSV - to the point where you can't 
tell an offset from the centre line of lots of GPS traces.  In some 
cases there are odd unexplainable offsets though.

The problem with Earl Sterndale though, is that it's at a place where a 
number of valleys meet - hills on all sides.  It's exactly the sort of 
place where there might be problems with any and all of OSSV and Bing 
imagery.  I've also seen (e.g. in Matlock) consistent GPS trace offsets 
on the side of a hill, so care even needs to be taken with those too.  
In Earl Sterndale though I'd probably trust the average of the GPS 
traces, as they're consistent along the roads and there's no obvious 
anomalies corresponding to hills or gaps in hills.

Looking here in Potlatch:

http://www.openstreetmap.org/edit?editor=potlatch2&lat=53.198777&lon=-1.863473&zoom=18

and looking the OSSV-drawn buildings against the Bing imagery and the 
underlying GPS traces, it does look like roads and buildings are offset 
maybe 5m to the south relative to traces.  Bing's maybe 2m to the south 
relative to GPS traces I guess?

Whether you'd worry about this or not is a different issue - knowing 
that the Quiet Woman pub is 1st on the left after the T-junction is 
useful; knowing whether that's 40m or 45m away isn't particularly more so.

Cheers,
Andy


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