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#1 2019-03-19 17:28:43

Happy Hobo
Member
Registered: 2017-08-19
Posts: 24

Aerial photos have inaccurate location?

In the IOS app “GoMap!!”, it seems that Bing aerials and OSM ítems disagree on location by about the same amount consistently.  For example, admin boundary 227019118 and items within.  I believe I have seen similar with Google Maps on ScribbleMaps.com.  Since my iPad doesn’t have GPS, I am unsure which to use to guide my additions and edits.

I’m no fan of Microsoft, but it’s hard to believe even they would be that wrong on something so simple.

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#2 2019-03-19 22:51:29

SimonPoole
Member
Registered: 2010-03-14
Posts: 1,786

Re: Aerial photos have inaccurate location?

Particularly global mosaics will have images from lots of different sources and will sometimes be misaligned, it is however way way better than it used to be.

Here's some indication on how to deal with the issue in JOSM https://learnosm.org/en/josm/correcting-imagery-offset/

In general you need to

* determine if the imagery, the OSM data or both have larger offsets (best against a large number of GPX traces)
* check if there is better aligned imagery available (now days we have access to 5-6 global layers and lots of regional ones)
* if all imagery is misaligned you need to align it before editing (that will depend on the app you are using)
* if the OSM data is off you need to decide on if it is bad enough to warrant moving the existing data (the answer to that really  depends on a number of factors).

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#3 2019-03-22 03:25:00

Rassilon
Member
Registered: 2018-10-31
Posts: 15

Re: Aerial photos have inaccurate location?

I usually use ESRI World Imagery (Clarity) Beta as my default background with no offset. In my experience it has better orthorectification and the seam stitching errors are much smaller than Bing. Bing also seems to have lens distortion which twists the image on the edges near the seam areas. The drawback with the clarity background is that, in my area at least, it is very old. In my state we had all our building footprints computer generated from Lidar scans and they almost always line up with the clarity background. Bing not so much.
But (using the iD editor) it looks like you have there in Spain a "PNOA Spain" background which lines up nice on that admin boundary you posted. I would use that.
https://www.openstreetmap.org/edit?edit … 5/-2.09839

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#4 2019-03-22 09:31:31

alan_gr
Member
Registered: 2017-11-27
Posts: 39

Re: Aerial photos have inaccurate location?

Rassilon wrote:

But (using the iD editor) it looks like you have there in Spain a "PNOA Spain" background which lines up nice on that admin boundary you posted. I would use that.

Good point, PNOA is used a lot by mappers in Spain and I would suggest not shifting anything relative to that unless you are really sure.

Interestingly in this location the two sets of DigitalGlobe imagery disagree with each other, with "standard" looking very similar to Bing and "Premium" aligning better to PNOA (and probably reality).

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#5 2019-03-24 15:53:28

Happy Hobo
Member
Registered: 2017-08-19
Posts: 24

Re: Aerial photos have inaccurate location?

I suppose I need to find another app.  Go Map I like, but it seems to limit me to Bing.  I also like Maps.me for the map itself, but as an editor, it sucks.

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#6 2019-03-24 17:28:29

Rassilon
Member
Registered: 2018-10-31
Posts: 15

Re: Aerial photos have inaccurate location?

After doing the short tutorial for the iD editor you can start mapping easily. I am always amazed at how easy it is for newcomers to learn it and be productive.

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#7 2019-03-24 19:37:36

wowik
Member
From: Zelenograd
Registered: 2009-09-29
Posts: 8,322

Re: Aerial photos have inaccurate location?

See also imagery offset database
https://wiki.openstreetmap.org/wiki/Ima … t_Database

It can help you to get o share imagery offsets with other mappers

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