Aspect Ratio
The aspect ratio of an oblate spheroid/ellipse, b:a, is the ratio of the polar to equatorial lengths, while the flattening (also called oblateness) f, is the ratio of the equatorial-polar length difference to the equatorial length:
These are just two of several different parameters used to define an ellipse and its solid body counterparts, all of which are ultimately trigonometric functions of the ellipse's modular angle, or angular eccentricity.
The oblate spheroid is the approximate shape of many planets and celestial bodies, including Saturn and Altair, and – to a lesser extent – the Earth (with a = 6378.137 km and b ≈ 6356.752 km, providing an aspect ratio of 0.99664717, a flattening of 0.003352859934, and inverse flattening of 298.2572). It is therefore the most-used geometric figure for defining reference ellipsoids, upon which cartographic and geodetic systems are based.
Read more about this topic: Oblate Spheroid
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