Conventional International Origin—The Conventional International Origin (CIO) is approximately the average location of the point at which the Earth’s axis of rotation intersected the Earth’s surface during the years 1900-1905.

Conventional Terrestrial Pole—A point defined by reducing the astronomic latitude, longitude and azimuths to a single conventional pole. It is used to position the third axis of the Conventional Terrestrial Reference System and the WGS 84 Reference System. It is also the origin of the polar motion coordinate system.

Conventional Terrestrial System—A right-handed Cartesian coordinate system in which the positive X and Y axes lie in the mean equatorial plane, and the positive Z axis is the northern portion of a line through the Earth’s center of mass and the Conventional International Origin.

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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