Flattening

The flattening of a Spheroid (also called Oblateness) is denoted $\varepsilon$ or $f$. It is defined as

$$\varepsilon\equiv\cases{ {a-c\over a} = 1-{c\over a} & oblate\cr {c-a\over a} ={c\over a}-1 & prolate,\cr}$$

where $c$ is the polar Radius and $a$ is the equatorial Radius.

See also Eccentricity, Ellipsoid, Oblate Spheroid, Prolate Spheroid, Spheroid