How the Ellipsoid height (which is what GPS reports) relates to the geoid height (definition of sea level) and the orthographic height (altitude above mean sea level). Though many GPS devices say they report height above sea level, they are probably lying. <p> From <a href="https://support.virtual-surveyor.com/support/solutions/articles/1000261349-the-difference-between-ellipsoidal-geoid-and-orthometric-elevations-">support.virtual-surveyor.com/support/solutions/articles/1000261349-the-difference-between-ellipsoidal-geoid-and-orthometric-elevations-</a>
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