Hi. Heute habe ich mich eingeloggt und gesehen, dass die Straßenkarte von Emden nicht mehr mit Bing-Bilder übereinstimmen. Sie wurde einfach ein Stück verschoben. Wie stelle ich nun fest, was richtig ist?

Wie kann ich die Änderungen an einem bestimmten Objekt ansehen? Die Chronik zeigt nur große Flächen an.

Bin Neuling, entschuldigt bitte die "dummen" Fragen ;)

asked 10 Apr '12, 20:18

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joman
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edited 23 Apr '13, 03:09

aseerel4c26's gravatar image

aseerel4c26 ♦
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...which Google translate reckons is:

Hi. Today I logged in and I saw that the road map of Emden not agree with Bing pictures. It was simply moved a piece. How do I now realize what is right?

How can I view the changes to a particular object? The history shows only large areas.

(11 Apr '12, 00:14) SomeoneElse ♦
1

Is this the Emden that you're talking about? Although it's possible that both imagery such as Bing and GPS traces can be offset, a quick look at Emden suggests that it doesn't seem too far out. Could you post a link (the "Permalink" button at the bottom-right in view mode) to the place that's wrong?

(11 Apr '12, 00:24) SomeoneElse ♦

Yes, this is my Emden. Not a place is wrong, but the complete map - streets and buildings - was moved.

(13 Apr '12, 20:16) joman

Please first make sure that the objects are really at the wrong position and the Bing imagery has no offset in your area.

(19 Apr '12, 08:43) scai ♦

"make sure that the Bing imagery has no offset"

How can i do it?

(19 Apr '12, 20:06) joman

You say that "the road map of Emden not agree with Bing pictures". Can you give an example of a road that is in the wrong place (and tell us whether it's north, east, south or west of where it should be)?

(19 Apr '12, 23:34) SomeoneElse ♦

Looking at the harbor area it looks like Bing is generally west of the OSM data. Setting an offset of Easting 15.0 Northing 0 makes many things align better. See fore example way http://www.openstreetmap.org/browse/way/28544821 and the surroundings. But I don't know the area so I can't tell what is correct.

(19 Apr '12, 23:57) gnurk

Ah yes - about 5m difference between OSM and Bing at z18 and z19. Actually, lining up Bing with the GPS suggests that a lot of the OSM data for the harbour is a bit out too. There are relatively few GPS traces though, so it's difficult to be sure (though being a harbour it's flat, which rules out some sorts of error).

(20 Apr '12, 15:28) SomeoneElse ♦
showing 5 of 8 show 3 more comments

The approximate offset can be found by looking at GPS traces and GPS waypoints made over time (and objects drawn from them without using sat images). There definitely are offsets in some Bing images - everyone can't reasonably have the same systematical errors in their GPS traces year after year. The hard thing may be to find out which ways have been entered in OSM using Bing, and which one have been entered just from GPS traces - especially if the mappers haven't used the source=Bing tag.

There is a wiki page about this challenging problem:

http://wiki.openstreetmap.org/wiki/True_Offset_Process

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answered 19 Apr '12, 20:57

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gnurk
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edited 19 Apr '12, 21:05

thank you very much

(20 Apr '12, 14:24) joman

(answering the second part of this) you can view changes to a particular object in edit mode by doing the following:

  1. Click the item
  2. Select "advanced"
  3. Click the mode or way number at the top left of the screen
  4. Click "more details"
  5. Click "View History" at the bottom of the new page that's displayed

You'll get a page like this.

or, from view mode:

  1. Hover the mouse over "Edit" and select "View Map Data"
  2. Click on the item that you're interested in.
  3. Click "Details"
  4. Click "View History" at the bottom of the new page that's displayed
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answered 11 Apr '12, 00:30

SomeoneElse's gravatar image

SomeoneElse ♦
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accept rate: 15%

thank you very much

(19 Apr '12, 20:04) joman

(following in from the comments above where gnurk pointed out a place where there was a clear offset)

Basically, the more data the better. The harbour area of Emden's pretty flat**, so I'd try and create some GPS traces by walking or cycling from the station past the yacht club (on top of the harbour wall if possible), round past the wind turbine as far as the sluice gate, and then back the way that you came. If you walk or cycle along the road, walk or cycle back on the other side of the road. If possible, do it again on a different day.

Then, in Potlatch or JOSM, you can load the GPS traces (it's worth looking at both just yours and yours together with everyone else's).

Your new traces will have long north-south and east-west components so in Potlatch or JOSM you'll be able to align the Bing background to them. Also, if your GPS traces agree with everyone else's then it's a good sign that they're correct. There are currently some OSM items (such as Schöpfwerkstraße east of the sluice gate) that don't seem to match existing GPS traces - it may be that the OSM ways are slightly offset, or that existing GPS traces are misleading because they're created by someone walking along only the one side of a road.

** in places that aren't flat or have high buildings it's possible to get systematic offsets on GPS traces, so alignment becomes more difficult.

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answered 20 Apr '12, 15:47

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SomeoneElse ♦
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accept rate: 15%

Zum ersten Teil der Frage (bitte stelle möglichst nicht mehrere Fragen in einer; den zweiten Teil ignoriere ich, ist ja auch nicht im Titel):

Luftbilder sind aus technischen Gründen nicht perfekt gegenüber der wahren Position ausgerichtet/kalibriert. Die Ausrichtung kann mit dem Ort und auch mit der Geländehöhe (bei Schrägaufnahmen) schwanken. Zusätzlich kann sie mit der Zoomstufe schwanken. Bei einer Aktualisierung der bing-Luftbilder kann es auch vorkommen, dass die Ausrichtung vorher eine andere war, als hinterher. Es ist annehmbar, dass die Ausrichtung nach einer Aktualisierung besser ist, als vorher. Sicher ist das aber nicht!

Deswegen sollte man vor dem Bearbeiten und Erstellen von OSM-Daten basierend auf Luftbildern immer die Ausrichtung prüfen und korrigieren. Infos:

Allerdings sollte man auch beachten, dass GPS auch mit Vorsicht zu benutzen ist:

Wenn keine GPS-Tracks auf dem Server gespeichert sind (du kannst sie üblicherweise mit den Editoren abrufen), dann bleibt dir nur selbst Tracks mit GPS-Geräten zu sammeln und dann die Ausrichtung zu korrigieren / zu bewerten.

Eine entsprechende englische Frage: bing-osm-and-my-waypoints-all-misaligned-who-do-i-trust

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answered 23 Apr '13, 02:38

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aseerel4c26 ♦
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accept rate: 17%

1

meta @ all: yes, I know that was already "answered" - but not in German. I think that, if possible, questions should get an answer in the language of the question (at least if the question is a common/good one) - for others (in this case).

(23 Apr '13, 02:43) aseerel4c26 ♦
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question asked: 10 Apr '12, 20:18

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last updated: 23 Apr '13, 03:09

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