Geodetic basics
| Task: Geometric spatial reference data (3D position, position and height) and physical gravity values must be presented in standardised, geodetic spatial reference systems, the so-called coordinate reference system. According to the ISO 19111 standard (Spatial Referencing by Coordinates), a coordinate reference system (CRS) consists of two components, the “datum” and the “coordinate system”. |
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| The datum, often also designated as the reference system, is the physical part of a CRS which establishes the reference to the Earth by definition of the zero point, the orientation of the coordinate axes and the scale. A datum can be a geodetic datum, a vertical datum or an engineering or local datum. Examples for a geodetic datum are the German Primary Triangulation Network (DHDN), also called “Potsdam Datum”, or the European Terrestrial Reference System 1989 (ETRS89). The coordinate system is the mathematical part of a CRS which establishes how coordinates are assigned to a geometry, e.g. a fixed point, using rules. The coordinates of a geometry can be stated, e.g. as Cartesian coordinates (X, Y, Z), ellipsoid coordinates (width, length and, where applicable, ellipsoidal height) or projected coordinates (Gauß-Krüger mapping, UTM mapping). As well as the CRS for 2D and 3D position data, some coordinate reference systems are defined for managing height data or coordinates (e.g. mean sea level heights). Transformations are necessary for the transfer of coordinates of a datum or reference system to another datum. | |