What Height System Should be Used in Geomatics

Abstract

The contribution is going to introduce first the idea of a height system as a conglomerate of the reference surface, a.k.a. a datum and properly defined heights. Then the kinds of height systems used in practice are going to be discussed. These are three: the Geodetic system consisting of the reference ellipsoid as a datum and Geodetic heights (also incorrectly often called “ellipsoidal heights”), the Classical system that consists of the geoid as a datum and Orthometric heights (above the sea level), and the Molodenskij system composed of the quasigeoid as a datum and Normal heights (referred to the quasi-geoid). The Geodetic system is used when heights are being determined by satellites, Classical system has been used throughout the world since individual nations introduced their national height systems and Molodenskij’s system is now being used in Russia and several European countries. Further, the question of realization of a height system in practice will be discussed. This discussion is going to deal with mean sea level (MSL), sea surface topography (SST), the way observed heights and height differences are transformed into proper heights and height differences and the role of gravity in these transformations, the role of potential numbers and dynamic heights. Next, the properties of height systems that make them appropriate for practice will be shown: first and utmost, the system must be congruent, i.e., the datum and heights taken together must give us, as closely as possible, the Geodetic heights, the heights must be holonomic to allow us to adjust loops of height differences and the system must be useful in practice.