Sketch of three coordinate systems: Geocentric Cartesian, Geocentric Geodetic, and Topocentric Cartesian

A sketch of three common coordinate system used to describe observations on the Earth, in particular in the field of gravimetry.

Geocentric Cartesian System: Z-axis coincides with the mean rotational axis of the Earth, the X-axis points to the Greenwich meridian, and the Y -axis completes a right-handed system.

Geocentric Geodetic System: Defined by a reference ellipsoid. The position of a point is defined by the geometric height h, the geodetic latitude φ, and the longitude λ.

Topocentric Cartesian System: Has an origin at a point P, axes x and y are parallel to the unit vectors v and w, respectively, and the z-axis is opposite to the unit vector u.

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