When determining the position of a point on the Earth within a three-dimensional space, one method is to use the Conventional Terrestrial (CT) coordinate system: a Cartesian coordinate system with x, y, and z axes.
In this coordinate system,
- The origin (0,0,0) corresponds with the mass center of the earth.
- The X axis is parallel to the Equator and points through the Greenwich Meridian (0° longitude). The Greenwich Meridian is also known as the Prime Meridian.
- The Z axis is coincident to the conventional terrestrial pole (C.T.P.) which was the mean position of the Earth's rotational axis between 1900 and 1905.
- The Y axis lies in the Earth's equatorial plane and is perpendicular to the X and Z axes and creates a right-handed Cartesian coordinate system.
The conventional terrestrial pole is commonly referred to as the Earth's North Pole.
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