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The reference ellipsoid that gives the best fit to the astrogeodetic network of a particular datum, and hence does not necessarily have its center at the center of the earth.



Related Terms

TRIAXIAL ELLIPSOID

A reference ellipsoid having three unequal axes; the shortest is the polar axis, and the two longer ones lie in the plane of the equator.

REFERENCE ELLIPSOID

A theoretical figure whose dimensions closely approach the dimensions of the geoid; the exact dimensions of the ellipsoid are determined by various considerations of the section of the earth’s surface of concern. Also called REFERENCE SPHER- OID, SPHEROID OF REFERENCE, ELLIPSOID OF REFERENCE.

GEODETIC MERIDIAN

A line on a reference ellipsoid which has the same geodetic longitude at every point

WORLD GEODETIC SYSTEM

A consistent set of parameters describing the size and shape of the earth, the positions of a network of points with respect to the center of mass of the earth, transformations from major geodetic datums, and the potential of the earth (usually in terms of harmonic coefficients). It forms the common geodetic reference system for modern charts on which positions from electronic navigation systems can be plotted directly without correction.

GEODETIC PARALLEL

A line on a reference ellipsoid which has the same geodetic latitude of every point. A geodetic parallel, other than the equator, is not a geodesic line. In form, it is a small circle whose plane is parallel with the plane of the geodetic equator.

GEOCENTRIC LATITUDE

The angle at the center of the reference ellipsoid between the celestial equator and a radius vector to a point on the ellipsoid. This differs from the geographic latitude by a maximum of 11.6' of ar

AXIS

  1. A straight line about which a body rotates, or around which a plane figure may rotate to produce a solid; a line of symmetry. A polar axis is the straight line connecting the poles of a body. The major axis of an ellipse or ellipsoid is its longest diameter; the minor axis, its shortest diameter. 2. One of a set of reference lines for certain systems of coordinates. 3. The principal line about which anything may extend, as the axis of a channel or compass card axis. 4. A straight line connecting two related points.

SUPPLEMENTARY ERROR

The error of a measuring instrument arising from the fact that the values of the influence quantities differ from those corresponding to the reference conditions.

ISO

International Standards Organization, sets viscosity reference scales.

DEAD-BAND

The variance between the reading of an operating measuring device (e.g. meter) and a reference device (e.g. prover) which is so small that there is no need for recalibration. The dead-band is smaller than the tolerance range. Dead bands are expressed as both + and - around the datum line.

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