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To define the position of points on the earth's surface we need geodetic reference systems. Reference system is a collective name for systems for determination of positions in one, two or three dimensions.
We distinguish between three basic surfaces
To state the location of points on the earth's surface, we need geodetic reference systems based on three basic surfaces, their interrelationships, and their changes over time.
- The earth's surface is the surface on which we normally stay. It includes the sea surface where there is sea.
- The geoid is the equipotential surface in the earth's gravity field that best connects to the sea surface.
- The earth ellipsoid is the rotation ellipsoid that best connects to the geoid. The ellipsoid is a mathematically simple model of the earth's shape.
Traditionally, the horizontal and vertical reference systems have been separated, but since we started using satellite technology for positioning, globally adapted three-dimensional reference systems are needed.
It is important to specify reference system
Since the position of a point can be given in different reference systems, it is important to always state which reference system the information refers to.
Lantmäteriet is the responsible authority
Lantmäteriet is responsible for management and maintenance of the national reference systems and geodetic control networks on a national level.
The national reference systems are SWEREF 99 in three dimensions and on the plane, RH 2000 in height and RG 2000 for gravity. To secure height measurements using GNSS, we are also responsible for the geoid model SWEN17_RH2000.
The geodetic control networks consist of points with precisely determined horizontal and vertical positions as well as gravity values.
Overview of Swedish reference systems (pdf, in Swedish, new window).
International cooperation
Reference systems are by their nature a global subject area and therefore international cooperation is a very important part in the development and management of reference systems.