Editing with Potlatch2 I have a problem with Bing background not being precise. To me it looks like the background map is "glued together" by two submaps and one of them do not fit precisely together with the other. South of a certain latitude everything looks OK, but north of the same latitude everything is off by several metres. Not easy to do the mapping. Can anybody help?

asked 21 Mar '12, 11:14

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Honning
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Any chance of a permalink to the problem area?

(21 Mar '12, 13:12) SomeoneElse ♦
1

Not sure how to permalink a Bing map, but here is a link to the area: http://www.openstreetmap.org/edit?editor=potlatch2&lat=59.51176&lon=10.68141&zoom=15

(21 Mar '12, 13:39) Honning

In panning around the area, it seems to be a somewhat localized issue with the imagery. To work around it, in Potlatch, you can hold down the space bar and move the imagery to realign it with the existing data.

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answered 21 Mar '12, 15:34

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neuhausr
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I was working with ajdusting the roads etc to the Bing imagery to make the maps more accurate. If Bing is not correct, am I making the maps incorrect? If I do a work around as you propose, what is then the idea to adjust maps to Bing?

(21 Mar '12, 15:52) Honning
1

You need some gps traces,ideally several in potlach2 youcan select others besides you own. Then if you are sure there's a mis alignment drag the bing to correct it. Searching these questions and the wiki on "bing" and "alignment" should help.

(21 Mar '12, 16:09) andy mackey

This is a related question about realignment http://help.openstreetmap.org/questions/6385/alignment-of-track-vs-background-imagery
The photos are "stuck" together and its more noticeable when the light as changed between pics.I have noticed when tracing over bing that the shadow of adjacent buildings occasionally points from a different direction,indicating a join, you could get a fairly precise time and date (or season) from the length of shadow and bearing but it's only of incidental interest. The images will be their most accurate in the centre, that is vertically below the camera the greater the angle from vertical the greater the distortion as the edges of images are further away from camera than the middle so they must stretch a bit. The higher the altitude the less distortion but the optics will need to be better and I suppose there will be some distortion for the greater depth of atmosphere that may have varying densities that will bend the light (as in heat shimmer). The wiki will I'm sure have some professional words on all of this.

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answered 21 Mar '12, 15:28

andy%20mackey's gravatar image

andy mackey
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One suggestion as to how to deal with this issue is the "True Offset Process", described here. As far as I know, there's no editor support for it (yet) and I would imagine that collating different people's impression of how much imagery is offset may prove difficult. In your area it's obvious that there's a discontinuity, but (especially in hilly areas) there can be problems with both imagery and GPS traces being (differently) offset. Even in non-hilly areas there can be problems (like here for example).

Basically, the more good GPS traces there are the better you can align imagery (and tell which GPS traces are good ones).

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answered 21 Mar '12, 17:20

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SomeoneElse ♦
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The existing traces seem to match the roads well so they are probably correct. It may be good to contact some more experienced local mappers and then agree on the realignment.After the main shift you could each correct the data that was drawn from ariel while it was misaligned. Hopefully as a shared task it would be less likely to upset other contributors and be less stressful than for a single mapper working alone.

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answered 21 Mar '12, 22:18

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andy mackey
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edited 22 Mar '12, 19:40

1

Thanks Andy. My main concern being a newbie is that I do not mess up the maps. How do I find an experienced local mapper?

(22 Mar '12, 07:53) Honning

Like you I normally use potlach2 but in the past I have installed and used JOSM which shows who as created the ways and nodes. This would show who as contributed in the area in question and they can then be contacted, I have been in the past, usually to point out my errors. I suggest you try searching these question about contacting mappers or ask new question "how to contact local mapppers"

(22 Mar '12, 19:25) andy mackey
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question asked: 21 Mar '12, 11:14

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last updated: 22 Mar '12, 19:40

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