Curious, is there a point (or points) of the earth that is the basis of Global Mean Sea Level (GMSL)?
I assume that is the median of the highest point of the earth, Mount Everest at 29,029’ and lowest, Challenger Deep at -35,994.1’?
But I guess this get’s even more complicated when factoring in gravity, weather, shifting of the oceans’ waves and terrain, etc. Geoid. So would GMSL be the median of highest point and lowest point on earth or more to it?
Geoid is the basis or zero elevation from what I understand.
So I guess I may or may not be answering my own question? Geoid is the basis of GMSL?
If so, what parts of the earth are at this location? Is there a global elevation Benchmark of the earth then for Orthometric Height for construction? Kind of like Greenwich, London is to time? (GMT).