[Tagging] building attributes

Martin Koppenhoefer dieterdreist at gmail.com
Wed Feb 8 16:48:21 GMT 2012





Am 08/feb/2012 um 17:03 schrieb John Sturdy <jcg.sturdy at gmail.com>:

> On Wed, Feb 8, 2012 at 12:40 PM, Martin Koppenhoefer
> <dieterdreist at gmail.com> wrote:
> 
>> 5. building:min_level=* Number of stories between ground and actual
>> first existing floor
>> -> I'd completely discourage usage of this key, and suggest to
>> estimate the elevation of the lowest part of the building.
> 
> This needs to take into account that some buildings are built on
> sloping ground, and the floor which is at ground level on one side of
> the building may not be on ground level at the other side.


Yes, this is a general problem here: reference elevation. I have thought about this, because if there are several building parts they might have different elevations to which there heights refer to. 

One solution might be to expressly tag this reference height. In Architecture you'd normally set the reference +-0.00 elevation in respect to a given ground elevation (which you choose freely, normally a point on the road, and which is given in the local height system). All other elevations are then relative to this 0. Each distinct object would have this reference height (it's 0.00 in WGS84) and it could even differ from the 0.00 of other building parts of the same building. This is essential as otherwise changing the ele of one object would have influence on the heights of other objects.

Cheers,
Martin


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