Knowra Geodesy Geodesy Geodesy measures Earth’s shape, gravity field, rotation, and surface positions. It establishes reference systems that make measurements consistent across regions and over time.
Geodetic datum : A reference system that defines how coordinates relate to Earth’s shape and position. Datums turn geodetic measurements into coordinates tied to a shared Earth model.
Reference ellipsoid : A mathematically defined ellipsoid used to approximate Earth’s overall shape. It supplies a smooth geometric model for latitude, longitude, and height.
Eratosthenes : An ancient Greek scholar who estimated Earth’s circumference from solar angles and distances. His calculation established an early geometric method for measuring Earth.
Global Positioning System : A United States satellite navigation system that provides positioning, navigation, and timing services. GPS turns geodetic satellite observations into widely used positions and timing.
International Terrestrial Reference Frame : A global realization of a terrestrial coordinate system based on measured station positions and motions. Maintaining its precision requires modeling tectonic motion, deformation, and measurement changes.
Global Navigation Satellite System : A system of satellites that provides positioning and timing signals to receivers on or near Earth. Satellite signals provide the distances and timing observations used for precise positioning.
Geoid : An equipotential surface of Earth’s gravity field that approximates global mean sea level. It provides the gravity-based reference surface behind many practical height systems.
Jean Picard : A French astronomer who made a precise seventeenth-century measurement of a meridian arc. His measurements helped sharpen estimates of Earth’s size and supported Newtonian tests.
National Spatial Reference System : The United States framework of coordinates, heights, gravity, and related geospatial reference data. It applies geodetic standards to surveying, mapping, and engineering across the United States.
Vertical datum : A reference surface and system used to define elevations or depths. Combining national height systems remains difficult because datums differ and evolve.
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