1-2 The Shape of the Earth

The shape of the Earth can be represented by an ellipsoid of rotation (or called a spheroid) with the lengths of the major semi-axis (a) and the minor semi-axis (b) as shown in Figure 1.4 (a).

The amount of polar flattening (or called ellipticity) is expressed by

The approximate values of the Earth are;

However, the major and minor semi-axes have been measured precisely by many scientists or organizations as listed in Table 1.1, that have been adopted in different countries.

The following coordinate systems are used to represent points on the surface of the Earth.

Geodetic Coordinator System (see. Figure 1.4 (b))

Longitude (l) is the angle measured from the Greenwich meridian. Latitude (j) is the angle measured between the equatorial plane and the normal line of the ellipsoid.

h: ellipsoid height

Geocentric Coordinate System (see Figure 1.4 (c))

Longitude (l) is the same as the Geodetic Coordinates.

Latitude (j) is the angle measured between the center and a point on the surface of the Earth under assumption that the Earth is approximated as a sphere with radius (R);