The cartesian coordinate system is a right-hand, rectangular, three-dimensional, earth-fixed coordinate system with an origin at (0, 0, 0). The Z-axis, is parrallel to the axis of rotation of the earth. The Z-coordinate is positive toward the North pole. The X-Y plane lies in the equatorial plane. The X-axis lies along the intersection of the plane containing the prime meridian and the equatorial plane. The X-coordinate is positive toward the intersection of the prime meridian and equator.