Hi Daniel,

> So you want to e.g. give the height of a bridge above the "mean high water
> spring" level of the river it crosses?

Yes.

> use a qualifier. The unit would be meter 

Yes.

> The "elevation" property we have (P2044) is defined to refer to NN

It is not a good idea, to define 'elevation'
like it is "defined" in P2044:
there are hundreds of reference-levels (not only NN)...

NN was used from 1879 to 1992 in Germany.

Now in Germany we use NHN !

In other countries there are different reference levels
changing in different epoches ...

> you would need a more general "elevation" property,
> and a "reference level" property to use as a qualifier.

Yes, every elevation needs a reference level.
(without a elevation measurement is not usable)

> Then you could express something like "elevation: 28.3m;

In WD there is a confusion between altitude and elevation?
(may be in American and British English?
or geographic and aviation and astronomy?)

> reference-level: Q6803625".

_reference-level_ could be:
'NN'
'NHN'
'LAT'
'MSL'
'MHWS'
and a lot of others...

But this is a combination of unit and reference-level:
'm ü.M.'

We should not mix or confound this modellings...

What will be the WD-way?
(you should discuss this with a geodetic specialist...!)

Additionally we need an expression for 'accuracy' and 'source':
If the hight unit is 'meter' and the source value is in 'feet',
the new value could have a lot more/less digits than the source,
but no better/worse accuracy...

Bests, Markus


> Am 27.09.2016 um 20:26 schrieb Markus Bärlocher:
>> Hallo Daniel,
>>
>> nein, ich suche nicht einen WP-Artikel über MHWS,
>> (diesen habe ich nur verlinkt als Erklärung)
>>
>> sondern eine Einheit/unit,
>> um MHWS als Bezugshorizont für geografische Höhen zu beschreiben.
>>
>> MHWS wird verwendet, um Brückendurchfahrtshöhen über Wasser zu
>> definieren, sowie für die geografische Höhe von Leuchtfeuern.
>>
>> Mit herzlichem Gruss,
>> Markus
>>
>>
>> Am 27.09.2016 um 19:28 schrieb Daniel Kinzler:
>>> Am 27.09.2016 um 19:10 schrieb Markus Bärlocher:
>>>> I look for this:
>>>> "Elevation in metres above 'mean high water spring' level."
>>>>
>>>> Which means the geographic hight above MHWS:
>>>> https://en.wikipedia.org/wiki/Mean_high_water_spring
>>>
>>> By clicking on "Wikidata Item" in the sidebar of that page, I get to
>>> https://www.wikidata.org/wiki/Q6803625 ("highest level that spring tides 
>>> reach
>>> on average over a period of time")
>>>
>>> Is that what you need?


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