[Tagging] [OSM-talk] [Spam?]Re: [Spam?]Re: Underground / hovering buildings

Peter Wendorff wendorff at uni-paderborn.de
Fri Feb 18 11:04:10 GMT 2011


Hi.
As Initiator and author of the proposal you refer to, let me explain, WHY:
Am 18.02.2011 11:16, schrieb M∡rtin Koppenhoefer:
> 2011/2/18 David Murn<davey at incanberra.com.au>:
>> Because the use of (min_)levels,height is in use by 3D renderers and
> IMHO this min_level-part of the advanced building proposal is not
> working (is using wrong semantics), at least for the illustration you
> can find in the wiki.
Is not working and "is using wrong semantics" is not the same.
>   building_levels should be the amount of building
> levels. If a building forms a "bridge" like in the illustration, where
> adjacent buildings have 7 levels, the "bridge" has only 2 levels and
> the 5 levels below are void, the proposal states you should still
> apply building_levels=7 and count the voids as levels.
You are an architect and from that perspective you are completely right.
My purpose with this design of the tagging scheme was something often 
applied in OSM: backwards compatibility.

Most people tagging level counts of buildings I think would not think as 
you describe for "bridges".
As bridges do not appear alone and instead are always part of a building 
including the sides of the bridge, the building as a whole would have 
been tagged with building_levels=7.
So far this obviously don't describe the bridge of course.
Now let's think about this bridge as a whole through the building block 
of 7 levels height.
And that's what the min_level does: it raises the bottom about the 
min_level count - in this example, it raises the bottom about 5 levels.

I played with the alternative more common for you, but what would that mean?
Only being able to interpret building_levels and not supporting 
min_levels would lead to false assumptions about the height of the 
building. A building with a roof above 7 floors would be interpreted as 
a building with height of 2 floors.
Let's stay at 3D-Rendering as the example application, you would have a 
U-shaped instead of a A-shaped building.
> This is against any common practise and definition in architecture,
yes, but not against interception of most people: Even a building with a 
tunnel at the basement level with 6 levels above is seen as a 
7-level-building.
And if you want to have the number of levels inside the building you can 
simply calculate it by building_levels - min_level.
> building law and the definition of building_levels in the wiki.
The definition of building_levels in the wiki 
(http://wiki.openstreetmap.org/wiki/Proposed_features/Building_attributes) 
states "Number of stories, including the ground floor".
My interpretation is: There is no explicit definition of the handling of 
"missing levels" like "tunnels".
But it's clearly stated "including ground floor". So I would say: it 
does not depend on the existance of a raised first floor.
Even for you as an architect I don't think that you define the first of 
the 2 raised floors of the example bridge is a "ground floor".
Please tell me, if I'm wrong.


regards
Peter



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