## 4 Reference system

03.323GPPRelease 98TSUniversal Geographical Area Description (GAD)

The reference system chosen for the coding of locations is the World Geodetic System 1984, (WGS 84), which is also used by the Global Positioning System, (GPS). The origin of the WGS 84 co-ordinate system is the geometric centre of the WGS 84 ellipsoid. The ellipsoid is constructed by the rotation of an ellipse around the minor axis which is oriented in the North-South direction. The rotation axis is the polar axis of the ellipsoid, and the plane orthogonal to it and including the centre of symmetry is the equatorial plane.

The relevant dimensions are as follows:

Major Axis (a) = 6378137 m

Minor Axis (b) = 6356752,314 m

First eccentricity of the ellipsoid

Co-ordinates are then expressed in terms of longitude and latitude relevant to this ellipsoid. The range of longitude is ‑180° to +180°, and the range of latitude is -90° to +90°. 0° longitude corresponds to the Greenwich Meridian, and positive angles are to the East, while negative angles are to the West. 0° latitude corresponds to the equator, and positive angles are to the North, while negative angles are to the South. Altitudes are defined as the distance between the ellipsoid and the point, along a line orthogonal to the ellipsoid.