Earth's rotation, internal density variations, and external tidal forces cause its shape to deviate systematically from a … See more

The following radii are derived from the World Geodetic System 1984 (WGS-84) reference ellipsoid. It is an idealized surface, and the Earth measurements used to calculate it have an uncertainty of ±2 m in both the … See more

The geocentric radius is the distance from the Earth's center to a point on the spheroid surface at geodetic latitude φ, given by the formula:
where a and b are, respectively, the equatorial r… See more

The Earth can be modeled as a sphere in many ways. This section describes the common ways. The various radii derived here use the notation and dimensions noted above for the Earth as derived from the … See more

The mathematical expressions above apply over the surface of the ellipsoid. The cases below considers Earth's topography, above or below a reference ellipsoid. As such, they are topographical geocentric distances, Rt, which depe… See more