[Tagging] RFC ele:regional

[Kevin Kenny]

On Mon, May 4, 2020 at 8:53 AM Greg Troxel <gdt at lexort.com> wrote:
> I'll also say that this alternate datum notion is irregular, in that we
> expect horizontal positions to be transformed from national horizontal
> datums to WGS84, and that putting in a tag to say that coordinates were
> in some other datum would be, I think, considered madness.  Instead, we
> expect people to transform any such data to WGS84.  (And we realize that
> meter level shifts are not that important usually, because measurements
> and source data is rarely that good.)

To muddy the waters further, while WGS84 included a geoid model,
virtually nobody uses it. It's been deprecated for over 20 years.

Elevations quoted as 'WGS84 elevation' (as opposed to
height-above-ellipsoid) are virtually always relative to EGM96,
Generally speaking, published topographic maps will cite separately
which horizontal and vertical datums they use. (Newer stuff might use
EGM 08, but the two agree to less than a meter almost everywhere.

Elevation as height-above-ellipsoid, unless you're using it in the
intermediate results of a GPS calculation, is nonsensical.

-- 
73 de ke9tv/2, Kevin