Flattening

The (first) flattening of a spheroid, also called oblateness or ellipticity, is defined as

(1)

where is the polar radius and is the equatorial radius.

It is related to the eccentricity by

			(2)
			(3)

(Snyder 1987, p. 13).

A so-called second and third flattening may be defined as

(4)

and

(5)

(Karney).