[Tagging] Let's get (quite) rid of units and their multiples in OSM values

Kevin Kenny kevin.b.kenny+osm at gmail.com
Mon Jul 30 16:33:33 UTC 2018


On Mon, Jul 30, 2018 at 11:39 AM Martin Koppenhoefer
<dieterdreist at gmail.com> wrote:
> I did not check any numbers, but I would also expect a lot of data not following this definition.
[of the ele=* tag meaining EGM96]


Uhm, yeah.  I've been using NAVD88 as orthometric datum. I have the
tables loaded in my
GPS app, and it's what surveyors use locally.  But the difference
between that and EGD96
is far too small for my equipment to measure - I don't have a
survey-grade GPS, or the
patience for the integration time that using one requires.

Entering ellipsoidal height rather than orthometric elevation, though,
is Just Plain Wrong -
and I bet we have a lot of data entered that way that are off by tens of metres.

I further bet that two-thirds of the people reading this thread have
Absolutely No Idea
what we're talking about. (That isn't really a severe criticism. It's
more an indictment
of the sorry state of consumer-grade GPS that ordinary mappers would
be forced to
learn that much geodesy to get it right.)



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