The coordinate system used by the GPS in the United States is a geodetic coordinate system. Its origin is located at the Earth’s center of mass, with the Z-axis pointing in the direction of the protocol Earth’s pole (CTP) defined by the BIH1984.0 epoch. The X-axis points to the intersection of the zero-degree meridian and the CTP equator as defined in BIH1984.0, and the Y-axis is determined according to the right-hand rule.
