Referenssielipsoid

A referenssielipsoid, or reference ellipsoid, is a mathematically defined surface that approximates the shape of the Earth. It is a prolate spheroid, meaning it is an ellipsoid of revolution generated by rotating an ellipse around its shorter axis. This shape is chosen because the Earth is not a perfect sphere; it bulges slightly at the equator due to its rotation. The referenssielipsoid provides a fundamental geometric basis for geodetic datums, which are used to define locations on the Earth's surface.

Various referenssielipsoids have been developed over time, each with slightly different parameters for its semi-major and semi-minor axes. These differences arise from varying measurement techniques and the specific regions or purposes for which the ellipsoid was designed. Common examples include the GRS 80 (Geodetic Reference System 1980) and the WGS 84 (World Geodetic System 1984). These systems are crucial for accurate mapping, navigation, and satellite positioning.

The parameters of a referenssielipsoid are typically defined by its semi-major axis (a), which is the distance from the center to the equator, and its reciprocal flattening (1/f), which describes how much the ellipsoid deviates from a perfect sphere. The referenssielipsoid is a simplified model, and the actual Earth's surface, known as the geoid, is a more complex and irregular shape that follows mean sea level. However, the referenssielipsoid serves as a practical and widely adopted reference for most geodetic applications.