ECEF stands for Earth-Centered, Earth-Fixed, and's a Cartesian coordinate system used for GPS, and's sometimes known as a "conventional terrestrial" system. It represents positions as an X, Y, and Z coordinate. The point (0,0,0) denotes the mass center of the earth, hence the name Earth-Centered. The z-axis's defined as being parallel to the earth rotational axes, pointing towards north. The x-axis intersects the sphere of the earth at the 0° latitude, 0° longitude. This means the ECEF… (More on Ecef)