A point in space may be located by referencing it to a known point. The known point is considered to be the origin of three mutually perpendicular lines which constitute what is known as a rectangular Cartesian coordinate system. The unknown point is then located by specifying the number of units along each of the three axes as measured from the origin. Additionally, a vector oriented at random in space whose tail is set at the origin may be resolved into its three components along the X, Y, and Z axes. Three coordinate systems, employing right-handed rectangular Cartesian axes, are generally used.
Z axes point along thumb, first and second fingers of right hand, respectively.
Resolution into components. Rectangular Cartesian coordinate system. In the Earth-axis system the Earth is considered to be flat and nonrotating. The X and Y axes lie in the geometric plane of the Earth, X pointing north and Y pointing east. The Z-axis points down toward the center of the Earth as shown in figure 164 .