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Ecef

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Title: Ecef  
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Subject: Horizontal position representation, Earth-centered inertial, Orthometric height, Geocentric coordinates, Geographic coordinate conversion
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Ecef

Earth Centered, Earth Fixed coordinates
Earth Centered, Earth Fixed coordinates in relation to latitude and longitude.

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

References

  1. ^ Alfred Leick, 2004, GPS Satellite Surveying, Wiley
  2. ^ http://www.gmat.unsw.edu.au/snap/gps/clynch_pdfs/coorddef.pdf
  3. ^ a b http://www.weblab.dlr.de/rbrt/pdf/TN_0001.pdf
  4. ^ http://metadata.dod.mil/mdr/ns/GSIP/crs/WGS84C_3D
  5. ^ 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
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