[OSM-talk] Bing imagery and the remap campaign

Andrew Errington a.errington at lancaster.ac.uk
Sat Feb 11 00:33:37 GMT 2012


On Sat, 11 Feb 2012 04:03:01 Douglas Musaazi wrote:
<snip>
> We shall also use this opportunity for the participants to re-map their
> previous edits and correct those that could have been mapped wrongly, and
> also agree to the new osm odbl licence.

Don't forget- sometimes Bing imagery is not accurately aligned.  You should 
double-check the alignment of the images before tracing from them.  Potlatch 
and JOSM have tools which will allow you to move the images to correct the 
alignment.

One simple way to do this is to make several GPS traces of a large and visible 
feature, such as a well-defined field, or a grid of roads, or an oval running 
track.  Make several traces on different days and get the best 'average' 
shape for this feature.  Next, turn on aerial imagery and check that the 
visible feature (which should be very clear on the image) lines up with the 
shape that you made.  If it does then you are lucky, and you don't need to 
realign the images.  If it doesn't, then move the aerial image layer until it 
lines up.

I have found that the offset from one area will work within a radius of about 
50km, but it's worth checking in different areas.

Best wishes,

Andrew



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