Clarify World Geodetic System 1984 and Earth-Centered Earth-Fixed Coordinate System

[alanruttenberg]

WGS84 encompasses both geodetic coordinates as well as Cartesian coordinates.

I believe what is called Earth-Centered Earth-Fixed Coordinate System is also WGS84 - that would be common usage, since this is an instance it can only be one CRS, as opposed to a class of such CRSs.

To clarify, consider renaming

World Geodetic System 1984 -> World Geodetic System 1984 geodetic coordinate reference system
or -> WGS84 geodetic coordinate reference system (e.g. EPSG 10605)

Earth-Centered Earth-Fixed Coordinate System -> WGS84 Earth-Centered Earth-Fixed Coordinate System
or WGS84 Cartesian Coordinate Reference System, and add Earth-Centered Earth-Fixed (and ECEF)
(e.g. EPSG 10604)

In addition add to the documentation of 'WGS84 geodetic coordinate reference system' that the coordinates are lat, long, and (optionally) height above ellipsoid and how lat and long are defined wrt to the Ellipsoid, similar to how x,y,z are documented for ECEF

You may or may not want to distinguish WGS84 geodetic 2d (EPSG 4326) from 3d (EPSG 10605). I don't simply omitting height when only the lat/long are known.

[alanruttenberg]

Also perhaps worth noting: The WGS84 coordinate system evolves over time, periodically releasing a new realization, e.g. EPSG 10605 is WGS 84 (G2296). These differ only at very high resolutions. The name for a representative standing in for all of them is "ensemble". You might want to add a scope note explaining the CCO terms are WGS84 ensemble, leaving room for extensions that might add the specific realizations. That there are multiple versions is why, when citing the EPSG ids above I write "e.g."

[alanruttenberg]

Tagging @JJBittner

[dr-shorthair]

Also see #759