Spheroid is the common name of the idealized ellipsoid model of the earth used in a geodetic datum. The surface of the earth (or even the gravitational surface of the earth) is not a perfect ellipsoid, but it is close enough for portions of the earth in order to adequately describe it as such.
The minimum two parameters needed to describe the ellipsoid model of the earth for all of the translation and projection equations are:
Equatorial Radius |
The distance (in meters) from the center of the ellipsoid to the equator. This parameter is sometimes designated as: a |
Inverse Flattening |
Indicator of how "squashed" the ellipsoid is. This parameter is sometimes designated as: 1/f |