Referenssielipsoidin

Referenssielipsoidi, often translated as reference ellipsoid or datum ellipsoid, is a mathematical model of the Earth's shape used as a reference surface in geodesy and cartography. The Earth is not a perfect sphere but rather an oblate spheroid, slightly flattened at the poles and bulging at the equator. A reference ellipsoid is a mathematically defined spheroid that best approximates this shape within a particular region or for a specific purpose.

Different reference ellipsoids exist, each defined by its semi-major axis (equatorial radius) and its reciprocal of flattening. Famous examples include the GRS 80 (Geodetic Reference System 1980) and the WGS 84 (World Geodetic System 1984). These ellipsoids serve as the basis for geodetic datums, which are systems that define the position of points on the Earth's surface.

The choice of reference ellipsoid impacts the accuracy of geodetic measurements, map projections, and satellite navigation systems. For instance, GPS uses the WGS 84 ellipsoid. By using a standardized reference ellipsoid, surveyors and cartographers can ensure consistency and compatibility in their work, allowing for the accurate representation and measurement of geographical information globally.