All,

Kinda of related to: this topic

I've been updating the very sparse map details for my own town recently and have moved on from iD to using JOSM which so far has been great. I've been using my own GPS tracks, surveying and cross referencing old out of copyright 1:2500 maps from the 1800's which I've geo-rectified with Global Mapper to give me accurate outlines of natural featurse that haven't moved in hundreds of years.

Bringing all that data into JOSM I can see that my town has been mostly aligned to the Bing imagery and is offset in various parts between 20-50 metres which is somewhat confirmed by the available public GPS traces.

I've been able to calculate the offsets of the Bing images and get all my references lined up in JOSM and as my town currently is very sparse (which I'm hoping to fix) I thought the best first step would be to get it aligned properly.

So to the crux - given the effort I'm putting into to getting it aligned, if a future contributor comes along and uses iD or JOSM with the default un-aligned Bing images I suppose there is a risk they'll "correct" my corrections.

Is there any method of sort of verifying my changes are based on accurate surveying to avoid someone re-aligning them to Bing or am I just at the mercy of whoever comes along after?

asked 04 Dec, 20:14

NeilJed's gravatar image

NeilJed
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accept rate: 0%

All,

Thanks for the tips. I think my approach will be.

1) Over the holidays I'll walk the field edges/outlines of key features with the OSM GPS Tracking app several times to get tracks for the features and upload them.

2) Add source:* tags where applicable to indicate where the data from the change came from.

3) Add fairly detailed description of why I moved the town in the change-log.

4) Calculate the Bing image offsets and upload them.

Luckily right now my town is just a grey outline and a bunch of roads so I don't see the initial correction being a huge task.

Thanks for the advice!

(06 Dec, 09:05) NeilJed

If you are willing to upload some of your additional gps traces (maybe after trimming) then that may help to stay the hand of anyone wanting to un-correct your edits. I'm not sure if iD shows these by default, but JOSM does and I imagine trying to realign a whole town in iD would be rather daunting anyway.

By the nature of the project we are always at the mercy of those who follow, but the more data you add the less likely it is for someone to move all of it to match the imagery.

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answered 05 Dec, 00:14

InsertUser's gravatar image

InsertUser
1.1k11723
accept rate: 18%

edited 05 Dec, 19:54

Also, while putting source:geometry=* on objects is rather uncommon these days (tags on the changeset being the current preference) it is not necessarily wrong and adding that to a few key ways might help to show someone that it's the imagery that is at fault.

(05 Dec, 00:23) InsertUser
4

Just to clarify, JOSM doesn't download traces by default. You can turn this on and it will remember that setting for future data downloads, but it isn't on by default.

(05 Dec, 16:58) alester

I stand corrected. It's been a while since I did a fresh install.

(05 Dec, 19:50) InsertUser

Although I don't think it's used in iD right now, there's this: https://wiki.openstreetmap.org/wiki/Imagery_Offset_Database

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answered 05 Dec, 04:59

yvecai's gravatar image

yvecai
1.2k922
accept rate: 12%

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question asked: 04 Dec, 20:14

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