Ned Co-Ordinate Frame - Advanced Navigation Spatial OEM Reference Manual

Spatial OEM Reference Manual
Page 16 of 88
Version 2.7
Equator
Illustration 11: World map showing latitudes and longitudes
Latitude and longitude give the 2D point on the surface of the Earth. These are combined with
height to give the 3D position on the Earth.
Height is the height above the WGS84 reference ellipsoid. The WGS84 reference ellipsoid is a
model used to approximate sea level across the Earth. Therefore the height should be considered
approximately relative to sea level. Due to the approximate nature of the WGS84 model, the
WGS84 height will not be the same as the actual sea level. For example, in Australia, the WGS84
height at sea level is 9 metres at some points.
2.8

NED Co-ordinate Frame

The NED (North East Down) co-ordinate frame is used to express velocities and relative positions.
The origin of the co-ordinate frame can be considered the current position. From that origin, the
north axis points true north and parallel to the line of latitude at that point. The east axis points
perpendicular to the north axis and parallel to the line of longitude at that point. The down axis
points directly down towards the centre of the Earth. See Illustration 12 for a graphical
representation of the NED co-ordinate frame at a position on the Earth.