ECEF ("Earth-Centered, Earth-Fixed"), also known as ECR ("Earth Centered Rotational"), is a geographic coordinate system and Cartesian coordinate system, and is sometimes known as a "conventional terrestrial" system. It represents positions as an X, Y, and Z coordinate. The point (0,0,0) is defined as the center of mass of the Earth, hence the name Earth-Centered. Its axes are aligned with the International Reference Pole (IRP) and International Reference Meridian (IRM) that are fixed with respect to the surface of the Earth, hence the name Earth-Fixed. This term can cause confusion since the Earth does not rotate about the z-axis (unlike an inertial system such as ECI), and is therefore alternatively called ECR.
The z-axis is pointing towards the north but it does not coincide exactly with the instantaneous Earth rotational axis. The slight "wobbling" of the rotational axis is known as polar motion. The x-axis intersects the sphere of the Earth at 0° latitude (Equator) and 0° longitude (Greenwich). This means that ECEF rotates with the earth and therefore, coordinates of a point fixed on the surface of the earth do not change. Conversion from a WGS84 Datum to ECEF can be used as an intermediate step in converting velocities to the North East Down coordinate system.
- Geodetic system
- Earth Centered Inertial coordinate system
- International Terrestrial Reference System (ITRS)
- Orbital state vectors
- ECEF datum transformation Notes on converting ECEF coordinates to WGS-84 datum
- Datum Transformations of GPS Positions Application Note Clearer notes on converting ECEF coordinates to WGS-84 datum
- Geodetic Datum Overview Orientation of the coordinate system and additional information
- GeographicLib includes a utility CartConvert which converts between geodetic and geocentric (ECEF) or local Cartesian (ENU) coordinates. This provides accurate results for all inputs including points close to the center of the earth.