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The semi-major axis (major semiaxis) is the longest semidiameter or one half of the major axis, and thus runs from the centre, through a focus, and to the perimeter. The semi-minor axis (minor semiaxis) of an ellipse or hyperbola is a line segment that is at right angles with the semi-major axis and has one end at the center of the conic section.
The reference ellipsoid is usually defined by its semi-major axis (equatorial radius) and either its semi-minor axis (polar radius) , aspect ratio (/) or flattening, but GRS80 is an exception: four independent constants are required for a complete definition.
The parameters determined are usually the semi-major axis, , and any of the semi-minor axis, , flattening, or eccentricity. Regional-scale systematic effects observed in the radius of curvature measurements reflect the geoid undulation and the deflection of the vertical, as explored in astrogeodetic leveling.
Why are they "semi-major axis" and "semi-minor axis" instead of "major semi-axis" and "minor semi-axis"? The prefix "semi-" should modify the noun "axis" rather than adjectives "major"/"minor" because these terms are about the largest and smallest half-axes, not the (full) axes that are "partly largest" and "partly smallest".
When increases from zero, i.e., assumes positive values, the line evolves into an ellipse that is being traced out in the counterclockwise direction (looking in the direction of the propagating wave); this then corresponds to left-handed elliptical polarization; the semi-major axis is now oriented at an angle .
The World Geodetic System (WGS) is a standard used in cartography, geodesy, and satellite navigation including GPS.The current version, WGS 84, defines an Earth-centered, Earth-fixed coordinate system and a geodetic datum, and also describes the associated Earth Gravitational Model (EGM) and World Magnetic Model (WMM).
The semi-major axis (a) and semi-minor axis (b) of an ellipse. According to Kepler's Third Law, the orbital period T of two point masses orbiting each other in a circular or elliptic orbit is: [1] = where: a is the orbit's semi-major axis; G is the gravitational constant,
Letting t = P, the orbital period, the area swept is the entire area of the ellipse, dA = π ab, where a is the semi-major axis and b is the semi-minor axis of the ellipse. [8] Hence, =. Multiplying this equation by 2,