OpenStreetMap
Bing image alignment and conferring with Google Earth
Posted by imroy on 2 September 2011 in English.I made my first real contribution the other day by using Potlatch 2 and the Bing imagery to add the pond in the Cowra Japanese Garden. I plan to go there later this month for their annual Sakura festival. We don't get a lot of that sort of stuff in rural Australia.
Anyway, I have two issues. Firstly is Bing image alignment. All of the roads around the Japanese garden are offset by a few metres compared to the Bing aerial imagery. Should I try to duplicate this offset in my edits? And should I realign surrounding roads, etc? I'd like to at least add the parking lot, which is just an extension of the access road. So I'm not sure what to do about that.
Secondly, I tried tracing some of the foot paths within the garden, but they're not so clear in the Bing images. So I checked in Google Earth, where they're much easier to see. But is this then considered a derived work? I'm not tracing the Google images, but I am using them to help me make sense of the Bing images. Certainly on some of the paths I couldn't have traced them if I had only used the Bing images. So I'm leaving that for now.
Discussion
Comment from AndrewBuck on 2 September 2011 at 13:25
You can re-align the imagery in potlatch. In potlatch 1 (probably the same in 2) you hold down the spacebar and then drag the background to its new location.
As for your question about Google, I really don't know. I think its pretty borderline, and I confess I've done similar things when working with imagery from the ISS. I used the ISS imagery as a source for what I was tracing but wasn't sure is some white blobs were oil tanks, I then confirmed that on google, although I can't remmeber if I ever did go back and enter them or not.
I think all in all it's best to try to stay away from google as much as possible, but it is definitely a grey area that you are referring to.
-Buck
Comment from Zverik on 2 September 2011 at 14:17
Bing imagery is offset in most areas, you need to align it to GPS tracks or to already drawn features. Looking at google maps is ok, as long as you don't use it as imagery layer to trace things.
Comment from Pieren on 2 September 2011 at 14:52
Agree, Bing imagery is offset by few meters almost everywhere. GPS tracks can be offset as well. But hey, Bing can be used for free in OSM ! This is something that was unbelievable when OSM started 7 years ago !
Ideally, you need a reference point somewhere on your map. By luck, in France, we have such survey points in many places and we can realign Bing by these few meters (but usually less than 2 meters). Elsewhere, you can do it yourself with special GPS stations or with multiple measurements made at different periods (using different satelites).
Bing positionning accuracy is very floating from one place to another.
About Google, Ed Parsons replied to our questions about such use (StreetView in that case) and he said : "checking the odd street names is OK.. but every street name I would suggest would represent a bulk feed."
So verifying some facts also displayed in Google picture is ok but doing this repeatedly would be a copyright infringement. (and this is only to check facts, not tracing over aerial imagery which is reusing alignment and georeferencing and that's not allowed). See this archive: http://lists.openstreetmap.org/pipermail/talk/2011-April/057473.html
Comment from maxolasersquad on 2 September 2011 at 19:47
I only look at Google imagery to compare works. Sometimes I'm curious how others decided to map something interesting.
If I see something on the other maps that would spark me to change my OSM maps, then I got visit that site personally to verify in person that what I'm mapping is current, and so that I ultimately end up building the final map based on my personal work, not on someone else's proprietary work.
On that note, I've found errors in professional maps, such as street names, that if I would have copied over, would have not only been infringement, but would have been adding an error into our free database.
Comment from imroy on 4 September 2011 at 11:18
Thanks for all the advice everyone! I'm going ahead with tracing as much as I can, using Google Earth to pick out features that aren't so clear on the Bing images. But I'll try to keep to an absolute minimum the amount of information only coming from Google.
And when I do visit the garden later this month I'll try to get a highly accurate fix on a reference point using a "GPS Average" app I have on my phone. That way I can sort out the Bing offset problem.
Comment from inas on 4 September 2011 at 20:44
If it isn't visible on bing, and we don't have a survey trace, then the question is always going to be how the information was derived.
This isn't so much about copyright, as breaching Google's terms of use. We don't want to end up with a tainted OSM. Survey the site, align the bing imagery.
Think of what you could legitimately place in the source tag. If you could place source=bing, or source=survey, then okay. If you would have to put source=google, then just forget it.