Reference systems for coordinates and heights

Reference systems for coordinates and heights are the basis for all geospatial information. Without them, it is not possible to unambiguously represent the location of an object. One of the main tasks of the Finnish Geodetic Institute is to create and maintain national coordinate and height systems in Finland.

EUREF-FIN coordinate frame is based on a large set of control points, which all are measured using satellite positioning.

The Finnish Geodetic Institute has created reference systems for Finland, such as the National Grid Coordinate System (KKJ), EUREF-FIN, N60, and N2000. The KKJ was created using triangulation measurements: angle and distance observations, baseline measurements, and astronomical observations. In order to create the vertical coordinate (height) reference systems N60 and N2000, both nationwide levellings and gravity observations were needed. In the past, the use of reference systems was often local. Today, the development of satellite positioning and increasing international connections require the systems to be fixed to global reference systems. For instance, EUREF-FIN (the Finnish realisation of the European-wide ETRS89 system) was created and tied to a global coordinate reference system using satellite positioning. Respectively, the new Finnish N2000 height system was tied to the datum (zero) point of the European EVRS system.

An adjustment computation of an international levelling network establishes a height system. Levelled lines with the fixed point NAP (Normaal Amsterdams Peil) are depicted in the figure. The red contours depict the land uplift model NKG2005LU (in millimetres).

To keep the reference systems precise and up-to-date, they need to be re-measured regularly or otherwise maintained. Globalization and the increased accuracy of current observation techniques require that changes and motions of the Earth need to be observed more precisely than before. For instance, tectonic motions change the positions of the benchmarks, and without continuous maintenance, the high accuracy achieved through satellite positioning deteriorates quickly with respect to the benchmarks. As a special phenomenon for the Nordic countries, the intraplate deformations of the Eurasian tectonic plate, caused by the postglacial rebound, are changing the relative positions both in vertical and horizontal directions in addition to the rigid plate motion. Monitoring these motions is an essential part of the work of the Department of Geodesy and Geodynamics.