On 2020-05-08 11:33, Martin Koppenhoefer wrote:
It could be useful when mapping something like a building. You could
establish a certain elevation as local zero (e.g. the elevation of the
ground floor) and have all other levels based on this. It is something
that could also not be needed because of an editor who abstracts this
(no need to store relative information if some frontend could do it),
but I would not hinder people from experimenting with it.
I can see wanting to do this, but I think it should not use the ele=
tag, and this really feels like it needs to be "height above ground
floor" or something. It really needs a scheme that is well thought
out. I too think it's fine if people do this, as long as they don't
use the ele= tag, which means something else.
> ele:regional is about admitting that you don't know
But, it asserts that the value is in some particular datum, and that you
can tell which one from knowing the area. All of this is untrue.
maybe a particular datum can not be given, but you can be quite sure (as
sure as you are willing to accept from a tag which pretends it is) it is
one of those common in the area (which also will not differ a lot,
probably).
I think we now know that the existing datums don't differ much from
WGS84 except Belgium, and given the EVRF2007 datum, it seems clear that
Belgium now will have that and the old one, differing by 2m.
Hence the thing we need to know, we don't, in this case.
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