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The map for the whole area around me, I am talking tens of kilometres, has an offset from the GPS. It matches Yahoo but does not match Bing or Google where as my GPS does tie in with those. The offset seems to be around 5-15 metres. I need to do some work to confirm the offset over a decent area, make some careful tracks at clear reference targets. What are people's thoughts on my trying to pull the whole area over to match the GPS? I want to try and get this sorted out as when I try and do a correction to a mistake I am ending up with a mismatch and trying to add new areas wont tie in with the existing parts. |
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You need lots of traces of the area (or is it well traced already) to get a good average as sometimes a trace will have an offset. You could give us a link to the area for second and third opinions as well. Look at these questions as well http://help.openstreetmap.org/questions/6385/alignment-of-track-vs-background-imagery and http://help.openstreetmap.org/questions/11380/bing-imagery-problem |
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One thing that you can do, if you're confident with your GPS accuracy, is to select three good spots around the area that makes up a triangle (doesn't have to be exactly equilateral). Make sure the spots is on high ground and/or open, and easy to make out from the bing photos (Center point of a soccer pitch isn't too bad) then wait til you have around 2 m accuracy before you start recording. Let the GPS lie still for at least 10-15 min (or an hour if you have the time). Then stop recording and go to the next spot. Then you can move the areal photo in JOSM to match the GPX-traces (blobs) of the spots, if it's impossible then either you GPS isn't very good or the areal is badly stitched. It is also great if you do this at a time when the conditions are good, both weather- and satellite wise. |
