[OSM-talk] License Change View on OSM

Andrew Errington a.errington at lancaster.ac.uk
Wed Dec 14 00:02:56 GMT 2011


On Tue, December 13, 2011 23:17, Jo wrote:
> I'm also taking the opportunity to align all the other features on bing.

Have you checked the local alignment of Bing aerials?  Where I am they can
be offset by as much as 20 metres!  I have to realign the aerial photo
layer before tracing anything from Bing.  The same problem was present in
Yahoo! aerials, but the offsets were different.

Generally what I do is make several GPS traces around a very visible
object (such as a field, running track, monument or something) then I
average the traces to get a good outline.  Once I have the outline
accurately recorded in OSM I adjust the position of the aerial photos
until the physical object lines up with the OSM outline.  Then I can map
other things nearby.  I have found that a single adjustment can apply to
areas 40 km away, sometimes more, sometimes less.  Other people's GPS
traces are good for double checking the alignment further away.

Once I have a good alignment I record it in JOSM so I can re-use it again
later.

Best wishes,

Andrew




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