ortometriske

Ortometriske, in English commonly orthometric, is a term used in geodesy and surveying to describe a vertical measure that corresponds to height above a reference surface defined by mean sea level. The ortometriske height represents the distance along the local gravity vector (the plumb line) from the geoid to a point on the Earth’s surface. In practice it is the height used in many vertical datums and topographic representations.

In geodetic notation, orthometric height H relates to ellipsoidal height h and geoid undulation N through the relationship h = H + N, or equivalently H = h − N. The ellipsoidal height h is the distance to the reference ellipsoid (a mathematically defined surface), while N, the geoid undulation, is the difference between the geoid and the ellipsoid. Therefore orthometric height can be obtained by subtracting the geoid undulation from the GNSS-derived ellipsoidal height, using a gravimetric geoid model.

Measurement and determination typically involve a combination of GNSS or leveling data and a geoid model. GNSS provides h, and geoid models (such as EGM2008 or more recent models) supply N for converting to H. Local surveys may also perform traditional leveling to establish a precise orthometric height, especially where high accuracy vertical datums are required.

Applications of ortometriske heights include civil engineering, construction, and topographic mapping, where heights are referenced to mean sea level. The concept is fundamental to vertical datum definitions, height networks, and the integration of GNSS with traditional leveling.