geodesi

Geodesy, or geodesi, is the science that studies the Earth's shape, its orientation in space, and its gravity field. It seeks to determine quantitative properties such as the size and shape of the Earth, the position of points on or near the surface, and how the Earth's mass distribution affects gravity and rotation. Geodesy provides reference frames and vertical and horizontal datums that underpin mapmaking, navigation, and Earth observation.

Historically, geodesy emerged from surveying and astronomy and progressed from simple triangulation to modern satellite-based measurement. It combines techniques from geodesy, geophysics, and astronomy to build accurate representations of the planet.

Key concepts include the reference ellipsoid, which approximates global shape; the geoid, an equipotential surface that represents mean sea level extended under continents; and terrestrial and celestial reference frames such as WGS84 and the International Terrestrial Reference Frame (ITRF). Geodesy also studies gravity anomalies and Earth's rotation parameters.

Major methods and instruments include triangulation and trilateration for relative positions, precise leveling for vertical measurements, gravimetry for gravity field, and satellite-based techniques such as GNSS (Global Navigation Satellite System) positioning, satellite laser ranging, and InSAR. Observations are processed to produce coordinates, altitudes, and time series of crustal motion.

Applications span cartography, land administration, navigation, space geodesy, construction planning, and climate studies, including sea-level change and earthquake monitoring. The discipline is coordinated by international bodies such as the International Association of Geodesy (IAG) and national geodetic surveys.