Measuring the World
Why Elevation Follows Gravity: The Geoid Beneath Every Height
GNSS measures height above a mathematical ellipsoid, but practical elevation depends on gravity, the geoid, and a physical definition of level.
From the Index
Tag: Vertical Datums
Reports, histories, and working notes filed under this subject.
Measuring the World
Finding Level: From Water Levels and Spirit Bubbles to Digital Heights
Establishing height has always required a definition of level, a reliable sight line, and a path of observations strong enough to reveal accumulated error.