Partially finished realigning buildings in Kota Bharu, Malaysia. It seems that a new sat image was available, and a mapper(s) traced the highways according to the new image but leaves the outline of buildings from older image intact. Therefore, those buildings have to be moved manually by selecting each one of them to align with the new image. (ignore lat long accuracy for the moment).
Perhaps, anyone who discovers an area with new sat image should first align existing hiways/buildings. Once the hiways/buildings matched with the new sat image, only then the sat image & hiways & buildings be offset to the accurate position. (can also be done the other way around, align the image to the existing highways/buildings, whichever is more accurate). That way we don’t have to align things two or three times manually. (Anyway, anybody knows how big an area is offset when we realign a sat image? One tile, 10sqkm, whole state?)
Or perhaps, people should try not to accidentally realign the map (new mappers especially).
Discussion
Comment from naoliv on 3 September 2015 at 12:17
“Perhaps, anyone who discovers an area with new sat image should first align existing hiways/buildings.”
No!
Sometimes the new imagery is slightly wrong. It’s always necessary to use GPS tracks to verify (or align) the imagery.
Comment from joost schouppe on 3 September 2015 at 16:21
To add to naoliv, what to do when you stumble upon an area where existing elements do not align current sat pic? The best is of course to align old and new elements correctly. But if there are no (or not enough) GPX traces available, it might be best to shift the sat pic according to the old data. Maybe previous mappers had something more to work on, like private gps tracks. If you’re convinced the new picture is better, it’s probably easier to adjust all existing elements first, and only then start mapping new things. Of course, the worst option is to ignore the problem, and have different adjustment for old and new stuff. I kind of messed things up like that in El Alto, Bolivia when I added huge suburbs; it’ll be quite some work to fix that up.
Comment from Zverik on 3 September 2015 at 18:54
Relevant links: http://wiki.openstreetmap.org/wiki/Imagery_Offset_Database http://wiki.openstreetmap.org/wiki/Imagery_Offset_Database/Quick_Start
(not available for iD yet)
Comment from AkuAnakTimur on 4 September 2015 at 04:18
It was me - did some work over the area (this mid-January), I tried to align the highways first. Moving (all) the buildings manually however… can be laborious. Need full focus (and also limitless internet usage quota - this problem is on my side).
The “latest” satellite imagery is from April 2012. I have kept tab on that based on my changeset - only to find out that Microsoft (Bing) re-added the older imageries which have been removed. So there’s no fresher imagery :(
How could I describe this… the April 2012 imagery is however is available up to zoom level 18 and only available near Kota Bahru (with respect to the whole of Kelantan state). Last time I did some work over there, if someone tried zooming to level 19 and above, the older imagery (from May 2005) will show up. As I am typing this, Bing aerial imagery will not be doing so - zooming in to higher levels (19+) yields nothing.
In addition, I have done the road alignments first, according to my private tracks, public tracks and Strava heat map. The more recent imagery is quite accurate, but the older imagery is not. I have lost my calibration apparently (I have to reinstall JOSM one time). My bad, I am not able to finish moving the buildings to a more accurate position. Need someone with better focus to complete that however…
That is really subjective. I have just recently adding things over here. Really blessed that this place managed to get OK-ish satellite coverage (March 2013 to the east, January 2012 to the west) but traces from the older imagery has to be realigned…
Comment from AkuAnakTimur on 4 September 2015 at 04:21
should be the other way around :-/
Comment from kucai on 4 September 2015 at 13:18
perhaps a little clarification to my post.
I am just proposing possible approaches to aligning existing trace to new sat images. I even mentioned, at the end of the process, the need to offset everything accurately, be it averaged gps traces or geodetic survey data.
If there are no gps traces available (quite common around here), then, i dont think it mattered much since nobody knew for sure which sat imagery is more accurate..I’ll just make the map pretty.
Akuanaktimur, this is never intended against you. You are one of the best mapper ive met in osm malaysia.
thanks for the input guys/gals!
Comment from AkuAnakTimur on 7 September 2015 at 06:59
No hard feelings bro, hehehe!
Great, another thing to mention in the Malaysia Wiki page. Will do it some time.
Regarding the latest Bing satellite imagery, Microsoft will give some hints about it. Recently in Penang (last December I think), quite a chunk of hi-res imagery mysteriously disappeared, leaving Mapbox layer the only viable useful imagery. Areas near Sungai Petani too.
Took them a few more months, then found out the satellite imagery in the Penang area (and chunk of the most north-west region Perak) is back up again. Imageries from October 2013 - still ok. The freshest imagery across the whole peninsular I guess is somewhere near Taman Negara (sigh…) (http://bingcoverage.org/?lat=4.336740238798254&lon=102.42948532104492&zoom=13&l=osm)[from July 2014]. But bad news for Sungai Petani. No updated imagery, but old images from early 2008 re-appeared. So it is really hit-and-miss situation.
Comment from AkuAnakTimur on 7 September 2015 at 06:59
Oops. The link should be like this instead.