ISO 8855 ENU earth-fixed system 
 
Table 13. ISO 8855 ENU earth-fixed system 
 
The east axis (E) is perpendicular to gravity, perpendicular to the north axis and is in 
the east direction. 
The north axis (N) is perpendicular to the gravity vector and in the direction of the 
north pole along the earth’s surface. 
The up axis (U) is co-axial with the gravity vector, and positive in the up direction. 
 
 
 
Figure 6. ISO 8855 ENU earth-fixed system 
The ISO earth-fixed system is attached to the vehicle but does not rotate with it. The north and east axes 
are perpendicular to the gravity vector and north always points north. 
 
OxTS horizontal frame 
The OxTS horizontal frame (sometimes called the level frame) is attached to the vehicle 
but does not rotate with the roll and pitch of the vehicle. It rotates by the heading of the 
vehicle. The definition of the OxTS Horizontal frame is listed in Table 14 and shown in 
Figure 7.