[Tagging] RFC ele:regional

[Greg Troxel]

Peter Elderson <pelderson at gmail.com> writes:

> Why not use a datum:value pair?
>
> ele=[datum:]value
>
> datum: is optional. If you don't know, just leave it out. Data users can
> assume locally signed or known.

Becuase, as I have said many times and no one seems to be listening, in
OSM we have said that we use WGS84, and thus all elevations must be in
WGS84 (height above geoid), the same way that all horizontal coordinates
must also be in WGS84.

The very notion of putting in elevations in other datums is very
irregular, and it's a path to madness where data in OSM is in varying
reference systems and the data consumer then has to deal and transform.
It seems really obvious that the data should be in the standard OSM
datum and therefore correct.

This entire situation is really blowing up a situation of people who
want to simultaneously not be rigorous, by entering elevations that they
don't have any basis for trusting or knowing the datum, and to be sort
of appearing to be rigorous by labeling them in a way that isn't sound.

I think it's completely fair to have an extra tag that indicates the
elevation value is low quality, so that those mappers that know this and
those data consumers that know this can express and understand this.
But it's also very important for the simple case to remain simple.

Adding datum: into elevation means that every data consumer has to adapt
to the new rule, while ele:datum=<datum> does not - those that ignore it
are not harmed.


Other than your proposal making it difficult for data consumers, it
seems equivalent to ele:datum=<datum>.