this leaves a lot of areas that are mismatched in offset. for example, Spydeberg is mapped at no offset, but Hobøl is mismatched, halfway at no offset and lower areas are offset.

asked 08 May '20, 06:41

mtbboy1993's gravatar image

accept rate: 0%

Imagery can be offset quite a bit from reality. This is often worse in areas with large changes in elevation. The usual advice for OSM is to align the imagery you use to as many GPS traces as you can get your hands on as GPS is usually more accurate (although it also has problems if you can't see much of the sky).

The default imagery in Norway seems to be Norway specific orthophoto and may be more accurate than the typical satellite imagery, but I can't find any documentation in the wiki to verify this. I would not recommend displacing existing data unless you have a non-imagery based source to use as a reference.

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answered 08 May '20, 08:10

InsertUser's gravatar image

accept rate: 21%

I haven't tried using GPS for OSM yet, but I can see the GPS recordings are quite inaccurate, I wave looked in trailforks on my ridelogs, but also I am a abassador so I can see GPS recordings on the map when adding a trail, but it varies from ride to ride,there is a OSM background , but they seem to match good enough to the map of Askim so it's not too bad I guess, it's usually few cm to a meter, some times more, sometimes in some sections, sometimes GPS get crazy quite often the signal is bad, but I have seen several gps tracks and combined they seem to do ok. I have been in other cities, but I haven't recorded with gps in all of them. but it's difficult to tell which is more accurate.

But whole Askim has been mapped at zero offset and most of Spydeberg, but I have seen Mysen was mismatched, seems like different offsets were used. in Hobøl I see it's off set so much buildings are offset halfway to the right, so to match it to the rest of the work mappers have done other places will be a lot of work. if it's several meters of difference it's very notissable. of course not all areas are as much offset, in all places.

(09 May '20, 00:42) mtbboy1993

When you say, "but I can see the GPS recordings are quite inaccurate" what are you basing this on? There is often scatter with GPS data, but there is rarely any systematic error that persists over multiple days.

(09 May '20, 15:23) InsertUser

I mean on trailforks, I can see ridelongs, also can see other users tracks cus I have access to that, cus I am a ambassador, this is not on OSM, just I can see the OSM map background, so I can compare.

(10 May '20, 07:07) mtbboy1993

In Mysen for example I see a lot of things were mapped like if using different offset and that was in same area, some to the left some further up, a lot of mess too, but I solved those, it was only the city centre that was a mess, rest was decently matching witch the rest. I Live in Askim so I know the area well, better than the other areas. where I live GPS is always different, but sometimes is crazy, but most times it is within 1 or 2 meter of accuracy compared to the OSM map. looks like most things were mapped with Norway Orthophoto at zero offset.

(10 May '20, 07:13) mtbboy1993

definitely some scatter, but with all of combined, or most of ride logs, I see it it matches quite ok on for most part. But this is is stiff not available to public. but some of my ridelogs are, but my latest were quite inaccurate. as long as not zooming in too much it's good enough. I most of the areas local to me seem to be mapped with zero offset using Norway Orthophoto I don't know if was actually done, but matches it for the most part, So that's what I have been using. but areas that are not local to me, further out are more of a mess, also badly mapped too. so those I improved, but I did not work further with making everything match, it's mostly not too far off I guess. but combined with inaccurate, very rough mapping it can be quite a mess.

(10 May '20, 07:49) mtbboy1993

I now found the GPS overlay in OSM, SO I will check it out. but I haven't added any GPS tracks myself. I am quite new to OSM, but am a fast learner. But Most GPS tracks are quite old, and things have changed a lot. but I see most GPS tracks match quite well.

(10 May '20, 07:51) mtbboy1993
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question asked: 08 May '20, 06:41

question was seen: 449 times

last updated: 10 May '20, 08:03

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