# Earth Definitions for Land Surveyors

**Earth-centered Earth-fixed—**A right-handed Cartesian coordinate system whose origin is the Earth’s center of mass. The X-axis runs through the intersection of the equator and zero longitude, the Y-axis runs along a line through the equator and perpendicular to the X-axis, and the Z-axis runs through the International Reference Pole (IRP).

**Earth curvature-**-See *curvature of the Earth *[SURVEYING].

**Earth ellipsoid, mean-**^{1}An ellipsoidal body which has the same mass and the same rotational velocity, about the shortest axis as the Earth and the same value of the coefficient C_{2}(-J_{2)} in the representation of the Earth’s gravity potential by the Legendre series. ^{2}An ellipsoidal body whose surface is at constant potential and whose four defining constants are determined by an adjustment of more than four interrelated constants. ^{3} That ellipsoid which most closely approximates the geoid.

**earthwork—**^{1}The operations connected with excavations and embankments of earth in preparing foundations of buildings, in constructing canals, railroads, highways, etc. ^{2} An embankment or construction made of earth.

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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