gpx-ideas
GPX Ideas
Elevation
Some useful links:
Geoid vs. Ellipsoid: What’s the Difference?
by Propeller Aero
Mean Sea Level, GPS and Geoid
by Witold Fraczek Sep 2003
There are also several scanned versions such as the one on
scribd.com
How I created an API to correct GPS to Sea Level
by Paul Harwood Sep 2022
Trimble documentation refers to it as “Orthometric height in meters (MSL reference)”
See
GGA
and
GNS