Systematic shift between streets and aerial photo

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Systematic shift between streets and aerial photo

Kjell Inge Tomren
Hello!

I noticed there was a street name missing near my home and as my first edit i decided to add that name to OSM. The update was easy. I even did it from my tablet in bed this morning so i was inspired to do more. There are no numbers on the houses in my area, so i decided to register my own and I did it by pointing at my house in the background aerial photo and added the info for a house. But I noticed the position of the house was not correct vs the nearby streets.

After a closer look I noticed that there is a systematic shift between the streets in my area and the background aerial photo. Then I´m a bit stuck. Which is correct positioned? The street positions or the background aerial photo? How is it possible to correct a systematic error like this?

Here is a link to the area:

Best regards,
Kjlell Inge Tomren

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Re: Systematic shift between streets and aerial photo

Andre Engels
Both can be the case, but here it seems it's the streets that are correct, the photograph that is shifted - When I look at nearby http://cycleland.blogspot.nl/2014/05/different-modes-different-priorities.html and then load the GPS traces (in Potlatch), there are several traces, and all of them correspond to the openstreetmap data, not to the satellite image.

André Engels



On Sat, May 31, 2014 at 11:14 AM, Kjell Inge Tomren <[hidden email]> wrote:
Hello!

I noticed there was a street name missing near my home and as my first edit i decided to add that name to OSM. The update was easy. I even did it from my tablet in bed this morning so i was inspired to do more. There are no numbers on the houses in my area, so i decided to register my own and I did it by pointing at my house in the background aerial photo and added the info for a house. But I noticed the position of the house was not correct vs the nearby streets.

After a closer look I noticed that there is a systematic shift between the streets in my area and the background aerial photo. Then I´m a bit stuck. Which is correct positioned? The street positions or the background aerial photo? How is it possible to correct a systematic error like this?

Here is a link to the area:

Best regards,
Kjlell Inge Tomren

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Re: Systematic shift between streets and aerial photo

Andrew Errington
In reply to this post by Kjell Inge Tomren
On Sat, 31 May 2014 18:14:49 Kjell Inge Tomren wrote:

> Hello!
>
> I noticed there was a street name missing near my home and as my first edit
> i decided to add that name to OSM. The update was easy. I even did it from
> my tablet in bed this morning so i was inspired to do more. There are no
> numbers on the houses in my area, so i decided to register my own and I
> did it by pointing at my house in the background aerial photo and added
> the info for a house. But I noticed the position of the house was not
> correct vs the nearby streets.
>
> After a closer look I noticed that there is a systematic shift between the
> streets in my area and the background aerial photo. Then I´m a bit stuck.
> Which is correct positioned? The street positions or the background aerial
> photo? How is it possible to correct a systematic error like this?
>
> Here is a link to the area:
> https://www.openstreetmap.org/edit#map=18/62.45124/6.36599
>
> Best regards,
> Kjlell Inge Tomren

Generally it's the aerial photo that is in the wrong place.  They are not
always properly aligned, and even if they are, the alignment sometimes changes
when a new set of aerial photos is released.

If there are any GPS traces visible in your area then you can use them to add
roads and also to realign the aerial photos with 'real life'.  Note that GPS
accuracy is also not perfect, but if you have enough traces you can see
clearly where the roads actually are.

I use JOSM and there is an option for sliding the aerial photos around under
the map layer, and for saving the offset position.  Other editors have similar
options.

Glad you got started with OSM.  Please keep mapping, and have fun!

Best wishes,

Andrew

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Re: Systematic shift between streets and aerial photo

Clifford Snow
In reply to this post by Kjell Inge Tomren

On Sat, May 31, 2014 at 2:14 AM, Kjell Inge Tomren <[hidden email]> wrote:
I noticed there was a street name missing near my home and as my first edit i decided to add that name to OSM. The update was easy. I even did it from my tablet in bed this morning so i was inspired to do more. There are no numbers on the houses in my area, so i decided to register my own and I did it by pointing at my house in the background aerial photo and added the info for a house. But I noticed the position of the house was not correct vs the nearby streets.

After a closer look I noticed that there is a systematic shift between the streets in my area and the background aerial photo. Then I´m a bit stuck. Which is correct positioned? The street positions or the background aerial photo? How is it possible to correct a systematic error like this?

There is an option to fix the background image in iD. Click on the layers icon and then "fix alignment." However, for that you need a good reference. Since there are only a few gpx traces, you might need other sources. Strava (bike/run app) has a iD product in beta that uses their traces. You can see a demo and use their slide iD beta at http://labs.strava.com/slide/. They have something on the order of 200B gpx points. From looking at their traces it does appear that the the Bing image is offset.

Slide works with your existing OSM id. You might give it a try. Once you have the roads aligned with their gpx points you can use the roads to fix the image alignment in the OSM iD editor.

Clifford


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