Earth-centered, Earth-fixed coordinate system
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.[1] 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,[2] 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,[3][4] 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.[3] The slight "wobbling" of the rotational axis is known as polar motion.[5] 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.
See also
- Geodetic system
- Earth Centered Inertial coordinate system
- International Terrestrial Reference System (ITRS)
- Orbital state vectors
References
- ^ Alfred Leick, 2004, GPS Satellite Surveying, Wiley
- ^ http://www.gmat.unsw.edu.au/snap/gps/clynch_pdfs/coorddef.pdf
- ^ a b http://www.weblab.dlr.de/rbrt/pdf/TN_0001.pdf
- ^ http://metadata.dod.mil/mdr/ns/GSIP/crs/WGS84C_3D
- ^ http://www.iers.org/nn_10398/IERS/EN/Science/EarthRotation/PolarMotion.html?__nnn=true
External links
- 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.
- EPSG:4978