In the area I am currently editing data, the Bing imagery is offset slightly differently between zoom levels. So if I draw the ways to match the photo, then zoom in, the ways all look a little wrong.
If I define a new offset, it moves the imagery at all the zoom levels. Is there a way to shift just one zoom level?
Also, is it possible to change the zoom level at which it switches to different images? The high-zoom images are much higher quality. When I zoom out a couple of levels, the imagery switches to a lower-resolution, blurry image. I would like it to use the better images for a few more levels of zoom.
I can right-click and deselect auto-zoom, but then if I move too far I just get a black screen.
In my area (Chiang Mai Thailand) the higher res pics are aligned better.
They are still wrong though, just by less.
I left my GPS in the garden by my gate, which is visible on the Bing images, just left it logging for a few hours.
Then using that track (that wanders around by a few metres) I can offset the Bing image to within a few metres of the true point.
This obviously isn’t always possible and of course it’s only accurate for the Bing tile around my house.
For other tiles in the area, I try to pick an obvious landmark and stop there for a while and leave the GPS logging.
If you’re mapping in an area where you can’t get a real GPS track, then the only choice you have is to use the highest res Bing tile (imo)
Looking at the “Stratton area of Swindon” it looks like you are mapping zoomed right in, this Bing image is dated 2003/2007 (right click on the Bing image in JOSM, select “Show Tile Info”). Zoom out a couple of clicks and as you say the image alignment changes, this Bing image (zoomed out) is dated at 2011, (right click on the Bing image in JOSM, select “Show Tile Info”).
The best thing to do is download a large enough area including Raw GPS Data to see how far out of alignment each image is compared to the GPS data. Then offset the image to suit the GPS data, save the offset. Do this for both images (2011 and the older one) then swap between offsets as and when needed. Bit of a pain but a more correct way to do it. As DuiNui says move away from that area onto a new image and start all over again.
Regards
Bernard
For the offset the best is to have GPS tracks from different devices and different dates. One track might still have a systematic deviation due to the specific device and atmospheric conditions at the date tracked.
Well yeah if you wanna be super accurate you’d leave multiple devices in the same spot and log for as long as possible.
Lots of work has been done on averaging GPS readings over time, but iirc 24 hours is usually enough to get sub meter precision.
Over a few hours I got a track roughly circular that fit perfectly between my gate posts.
I think that’s more than good enough for OSM
