Sustainable development and digitalization need reliable data. Geospatial data becomes a more and more important tool in society for many kinds of research of immediate use, but also for future planning and enterprise. Harmonization of geodata is very important for data producers and organizations, e.g. for mapping agencies. Establishing a uniform horizontal/vertical reference system is a basic prerequisite for combining data from different sources, and for allowing cross-border presentations and analyzes. If we do not use the same reference for positioning, it is not certain that one can compose reliable geodata from different organizations.

The overall aim of this study is to provide a theoretical and practical solution to unifying height systems in order to overcome systematic datum inconsistencies in height data and digital terrain models. The study deals with a variety of issues in physical geodesy such as Earth’s gravity field, sea level rise, sea surface topography and GNSS data. The advent of satellite altimetry in the 1970s provided a tool for the realization of a global vertical datum as being the equipotential surface of the Earth’s gravity field that minimizes the sea-surface topography (SST) all over the oceans in a least-squares sense. This leads to a direct determination of the geoid potential (W₀) from satellite altimetry and an Earth Gravitational Model (EGM).  In contrast, here we will first determine the Mean Earth Ellipsoid parameters and from these follows W₀. This means that once the size of the axes of the globally best-fitting ellipsoid is determined, W₀ follows. A major problem with this method is that satellite altimetry is only successful over the oceans, but the method requires global data. This problem is solved by employing satellite altimetry and the EGM in a practical combination.