Hello. I'm new to OpenStreetMap and I have a question regarding aerial imagery alignment. When in edit mode, I notice that some buildings, roads, etc. are properly aligned with aerial imagery and others are not. Recently I discovered about imagery offset, the problem is it is useless since I mentioned that some things are properly aligned and others are misaligned, so when setting imagery offset, still some objects are misaligned. Also, I have no clue if I should tweak imagery offset, up until know, I didn't use it. It's very difficult for new users to have to deal this issue, OpenStreetMap is making it more difficult to make proper contributions. Also, I'm aware that I should use GPS traces as well for alignment, the thing is I have no clue how they work and in most areas of my country there aren't many GPS traces.

asked 04 Mar, 17:25

newbie12349's gravatar image

accept rate: 0%

Imagery layers have generally been warped to account for camera position and terrain, to varying levels of success. Unless you are in an area with a suitably licenced accurate government map layer the most accurate reference most hobby mappers have access to is multiple GPS traces over multiple days.

If you have lots of traces to rely on (or are able to record them) then try to align to the GPS traces, this may need frequent updating in hilly areas or if you have a bad seam. If you have nothing to go on, try to align the imagery to the existing mapping effort as best you can. As others have said, I would not recommend doing a wholesale move of existing data unless you are highly confident in the location you are going to move it to and have discussed the move with the local mapping community.

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answered 06 Mar, 23:28

InsertUser's gravatar image

accept rate: 20%

Hi newbie, as soon as you dig deeper into OSM and arial views, zoom levels and so on, you will notice that even zoom levels don’t present the same alignment. The only rule is stick to one arial view and the same level to work on. Have a look at other levels and arial views to obtain more information about the existence of objects and ways and move new or other objects to the original alligment you started on. Welcome, have fun and keep mapping.

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answered 05 Mar, 11:01

Hendrikklaas's gravatar image

accept rate: 5%


Don't start moving existing objects around unless you are pretty sure that the alignment of aerial imagery is sufficiently correct. This can only be ensured by comparing aerial imagery with multiple GPX traces. Looking at other imagery or existing objects won't help.

(05 Mar, 11:55) scai ♦

as I said most areas outside big cities in my country don't have any or enough GPS traces to be able to align imagery

(05 Mar, 19:25) newbie12349
(06 Mar, 18:03) andy mackey
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question asked: 04 Mar, 17:25

question was seen: 269 times

last updated: 06 Mar, 23:28

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