Knowra Figure of the Earth Figure of the Earth The figure of the Earth is its size and shape as represented in geodesy. It is approximated by a rotating oblate spheroid and refined by the geoid, an irregular surface of equal gravitational potential.
Geodesy : The science of measuring Earth’s shape, orientation, gravity field, and changing positions. This is the discipline that defines and measures Earth’s figure.
Reference ellipsoid : A mathematically defined ellipsoid used as a smooth reference surface for geodetic coordinates and calculations. It supplies the regular surface used to approximate Earth’s overall shape.
World Geodetic System 1984 : A global geodetic reference system defining an Earth-centered coordinate frame and reference ellipsoid, used by GPS. Its ellipsoid and coordinates make a global Earth figure practical for positioning.
Sphere : A three-dimensional surface whose points are all equally distant from a center. A sphere is simpler than Earth’s figure but ignores polar flattening.
Oblate spheroid : A spheroid flattened at its poles and bulging at its equator. It captures Earth’s broad flattening caused by rotation.
Earth's flattening : The difference between Earth’s equatorial and polar dimensions, commonly expressed as a ratio of equatorial excess to equatorial diameter. Flattening quantifies how far Earth departs from a sphere.
Global Positioning System : A satellite navigation system that determines position, velocity, and time using signals from orbiting satellites. GPS positions depend on a specified Earth-centered frame and ellipsoidal model.
Triaxial ellipsoid : An ellipsoid with three unequal principal axes. It allows unequal equatorial dimensions that a rotationally symmetric spheroid cannot represent.
Geoid : An equipotential surface of Earth’s gravity field that approximately coincides with mean sea level. It represents gravity-driven departures from a smooth reference ellipsoid.
Geodetic datum : A reference framework that defines coordinate origins, axes, scale, and an Earth model for positioning. A datum ties measurements to a selected ellipsoid and coordinate system.
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