[Talk-GB] building shapes from OS Street View

Ed Avis eda at waniasset.com
Fri Apr 9 18:33:03 BST 2010

Dave Stubbs <osm.list at ...> writes:

>London has a lot of buildings, but only in certain areas. What I don't want to
>have to do is wake up one morning to discover someone has helpfully
>imported auto-detected rectangles over the top, meaning I have to
>spend the next three days/years cleaning up the data. If all you want
>to do is load some buildings into an area (however that's
>implemented), fix it up to avoid duplicates and conflicts with
>existing data such as roads, and upload that, then fine.

I think it's safe to say that nobody is proposing to indiscriminately dump
buildings or anything else over the top of existing mapping.  That could only
be appropriate for almost totally unmapped areas.  Let's be sure that people
are not talking past each other: any 'import' or 'bulk import' would have to
be done with caution and plenty of checks against existing data, only adding
new information where it is clearly missing.  I think everyone accepts that.

Perhaps one rule of thumb would be not to import any building from OS within
100 metres of an existing building on the map.  The 'gaps' could be filled in
later with manual assistance.

Where it gets more interesting is when OS geometry differs slightly from our
own.  If the OS buildings were simply copied they could end up overlapping
streets.  Some subtle kind of warping might be needed to shift coordinates by
a metre or two so that the relative position of the building relative to the
roads is preserved.  (I would estimate that the precision of existing OSM
geometry is not more than that, given that GPSes give at best 2m precision
under ideal conditions and the aerial photos are not always perfectly aligned.)

Ed Avis <eda at waniasset.com>

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