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1. Elevation

   Linked via "geoid undulation"

   Geodetic Elevation and Datums
   In geodesy, elevation distinguishes between orthometric height and ellipsoidal height. Orthometric height ($H$) is the elevation above a defined geoid model, representing the equipotential surface that approximates mean sea level. Ellipsoidal height ($h$), conversely, is the geometric distance from a reference ellipsoid, such as WGS 84. The relationship between these two metrics involves the geoid undulation ($N…