While working on HOT Typhoon Haiyan mapping I noticed a whole area moved about 14m to the west while verify a job tile in task manager. Using JOSM I looked into the history of one node and found the changeset where the nodes were moved.

I noticed the user had only a few changesets. It could be that the user acciential moved the area. But I’m not sure, there may always be a reason. So I wrote a message to the user, tried to be polite and added the sentence «Under no circumstance this little critics should stop you from further mapping».

A few hours later the user responded with a elaborate answer, explaining he noticed an offset to the background and tried to fix it. He also noted that this wouldn’t stop him from further mapping. This was my biggest concern that he was offended.

It seems very reasonable. In the changeset I saw he used the JOSM editor, so it’s likely he accidentially added a aerial imagery offset. His other changesets all looked sane. I responded with some hints and offered to help.

We agreed that I fix it for him, so I’ve had my first case of a kind of revert. I checked the documentation to see what options are available. One seems to be the revert plugin for JOSM. Well I don’t really wanted to revert the whole changeset, I just want to move it back.

Fortunately I found the «Changeset Manager» in JOSM («Window» Menu). So it was easy to enter the changeset number, load the whole changeset. Then I downloaded the affected area, big enough to surely include the whole changeset. Then I added the Bing aerial imagery layer as reference. Finally I opened the changeset manager again, clicked the button «Select the primitives in the content of this changeset in the current data layer», and voilà, all moved items are selected. Now I had just to move the items back, using the background image as guidance. Of course a dialog popped up, warning me I’ve had just moved more than 20 objects: Yes I’m sure! Finally I upload the new changeset and add a sane commit message.

That was easy.



Comment from sonaptech on 19 November 2013 at 10:26

thanks you

Comment from Vincent de Phily on 19 November 2013 at 10:32

Well done, one often forgets the power of the changesets manager.

Not scaring new contributors away with a “you’re doing it wrong” message is very important. Some rules of thumb I use :

  • Be welcoming, thankfull, jovial.
  • Dont blame; label even attrocious mistakes as “things you could improve”.
  • Offer to help or explain further, and talk about alternate help sources (this link).
  • Fix the badly damaged or hard to correct bits yourself.
  • Explain (with wiki links if applicable) how to fix the rest (and fix it yourself after a week or two if there’s no reaction).
  • Finish on a “happy mapping” good-bye note.

Comment from malenki on 21 November 2013 at 07:54

Thanks to your writeup now I know of the changeset manager though I use JOSM since I started with OSM.

Because I haven’t heard of the changeset manager until now I would have tried to fix the offset this way:
* revert the changeset in question with the reverter plugin
* select the data with offset (by comparing to a data layer with the latest data or an up-to-date map-layer)
* upload only the selection

Maybe this short description helps you to dare with the revert plugin. :)

Comment from FTA on 30 November 2013 at 17:11

Thanks for the plug about the changeset manager! I’ve had a situation or two where I have needed to use something like this but couldn’t find an addon. Now I know :)

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