[Tagging] RFC ele:regional

[Colin Smale]

On 2020-05-03 13:05, Volker Schmidt wrote:

> Martin 
> I am not an expert, but it looks as if the Wiki page Key:ele [1] is not up-to-date. 
> I thought that WGS84 uses the EGM96 Geoid, named "WGS84 EGM96 Geoid".  Hence there should be no difference between WGS84 and EGM96 elevations. 
> 
> Also it would be helpful, f you could give examples of local elevation systems which would need explicit tagging. 
> When I see an elevation value on the ground I do not see any reference to the reference system, so I cannot know, as a mapper, what reference system is at the base of the informaton that I find on the ground. In that respect the proposal is not at all clear from a practical perspective.

I think most countries with a coastline commonly use "sea level" as the
vertical basis. The definition of "sea level" differs from country to
country of course. NL uses "NAP" (Normaal Amsterdams Peil; normal
Amsterdam level) whereas Belgium uses "TAW" (Tweede Algemene
Waterpassing; second general water-levelling) as its basis. The
difference is 2.33m, which might not be so important for the heights of
mountains but along the coast it is critical for the correct
understanding of water depths, tides etc. The Westerschelde estuary
flows through NL until just before it reaches Antwerp (Belgium). To
avoid expensive misunderstandings it is essential that all bathymetric
data, tidal data, bridge heights etc be very clearly labelled with their
datum. 

  

Links:
------
[1] https://wiki.openstreetmap.org/wiki/Key:ele
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