[Tagging] Quick Building tracing question... -> Area Selector JOSM plugin

André Pirard a.pirard.papou at gmail.com
Thu Jan 10 23:40:18 UTC 2019

On 2019-01-10 03:42, John Willis wrote:
> I am tracing and repairing existing traces of warehouses in an 
> industrial district.
On a slightly different but similar subject.
To do serious fast building tracing, one should use JOSM with Area 
Selector Plugin <https://github.com/JOSM/areaselector> and an 
orthorectified map such as PICC in geoportail.wallonie.be or 
basemap.at.  That goes, complete with auto-incrementing street number 
tagging, at the rate of one house per 5-10 sec, but needs occasional 
touch up with Improve Way Accuracy tool.
While doing that I also make lots of corrections to traces by other OSM 
editors with a 2, 5 m or more precision error.
This is partly because they trace roofs from aerial maps, which are not 
at ground location because the camera view and walls are slanted. But 
also the roads are affected by imprecision.
Orthorectification does an incredible job of putting that right, 
impossible to do by hand. It computes the slant angle in one place, uses 
it in another, uses shades on the ground etc. I've seen it detect in 
meadows banks (slopes) that were strictly invisible to the eye.
This raises a problem.
When meeting untagged buildings that have been coarsely traced 5-10 m 
away from their position, should they simply be erased and replaced in 5 
secs or should 20+ sec instead of 5 be spent for conflation?
I asked Paul to add conflation 
<https://github.com/JOSM/areaselector/issues/23>. He did it, but with no 
tag merging.
I suggested that Area Selector simply invoked Replace Geometry instead 
If you feel that conflation is important, please visit these pages and 
back these requests.
> Many of the warehouses have large (3-6m) roofs over the loading dock 
> gates, making the building appear bigger.
> here is an example.
> https://www.openstreetmap.org/way/494766956
> if I am mapping this kind of warehouses, which should I:
> - map the whole structure as a warehouse
> - map on the building portion as a warehouse (as I have done)
> - map the building as a warehouse and map an attached polygon as the 
> roof (which I haven’t done yet).
> I am going to spend the time cleaning up UltimaSnorlax’s bad polygons, 
> I might a well draw them correctly the first time.
> Javbw

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