[Tagging] RFC ele:regional

[Martin Koppenhoefer]

Am Mo., 4. Mai 2020 um 10:50 Uhr schrieb Simon Poole <simon at poole.ch>:

> Historically the understanding was that ele would use "height above the
> ellipsoid", there is some reasoning on the Altitude page, might have
> made sense originally. In 2013 the ele entry was fiddled to point to the
> height above geoid.
>


in 2013 the altitude page was not really created yet, there was only a page
in German which hardly can be seen as relevant for the global project. The
"key:ele" page already referred to the geoid rather than the ellipsoid in
September 2008, as it said "height above sea level":
https://wiki.openstreetmap.org/w/index.php?title=Key:ele&direction=next&oldid=125595
"Elevation (height above sea level) of a point in metres."

Generally, the "altitude" term does not seem to catch it at all, it appears
to mean a height _above_ ground, while with the "ele" tag and variations we
are aiming at recording the actual ground elevation.



This leaves us with
>
> a) conflicting definitions in the wiki (not the first time)
>
> b) a tag de-facto redefined after multiple years of use (natural=tree
> anybody?)
>


not really comparable, because "a tree" is very clear, "a ground elevation"
isn't (because it refers to a reference which isn't given)



>
> Naturally the correct way to solve the issue would have been to
> introduce a new tag with the appropriate semantics and then let ele die
> out. Given that the mess has already happened it could be argued that we
> might as well use ele with the semantics that have been proposed for
> ele:regional, because that is what it "mostly"* has been used for.
>


this would mean repeating the same mistake as 2013, continue to use the
same tag for which it was already discovered that the values are referring
to different references (well knowing, that not all values refer to the
definition, some are referring to the WGS84 ellipsoid, some are referring
to a geoid)


Cheers
Martin
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