Document MT0605P.E
© Xsens Technologies B.V.
MTi User Manual
26
4.2.3
Orientation data
The MTi calculates the orientation (DataID 0x2010, 0x2020, 0x2030) between the calibrated inertial
data and magnetic field, represented in
(S)
or
(O)
, and the local Earth-fixed coordinate system
(L)
.
By default the local earth-fixed reference co-ordinate system used is defined as a right handed
Cartesian co-ordinate system with:
X positive to the East (E).
Y positive to the North (N).
Z positive when pointing up (U).
This coordinate system is known as ENU and is the standard in inertial navigation for aviation and
geodetic applications. Note that it is possible to change the coordinate system using an alignment
matrix or orientation reset.
The 3D orientation output is defined as the orientation between the body-fixed co-ordinate system,
(S)
,
and the earth-fixed co-ordinate system,
(L)
, using the earth-fixed co-ordinate system,
(L)
, as the
reference co-ordinate system.
Interpretation of yaw as heading
4
Heading is defined as the angle between north and horizontal projection of the vehicle roll axis. Yaw is
defined for a particular local-level navigation frame as the angle from a horizontal navigation axis to
the projection of the longitudinal axis in the horizontal plane following the right-hand rule. Based on the
definition of heading and yaw, consider the use of the MTi in an aircraft which is stationary and
pointing north. Below, a table is displayed that shows the heading and yaw outputs for the three
reference coordinate system (available with MTi)
Reference coordinate
system
Direction of mounting,
aircraft pointing North
Heading value (not
outputted by MTi)
Yaw value
East-North-Up (ENU)
x-axis of MTi aligned with
vehicle (pointing North)
0 deg
90 deg
North-West-Up (NWU)
x-axis of MTi aligned with
vehicle (pointing North)
0 deg
0 deg
North-East-Down
(NED)
x-axis of MTi aligned with
vehicle (pointing North)
0 deg
0 deg
When using the ENU convention (default), the yaw output is 0º when the vehicle (x-axis of the MTi) is
pointing East. When it is required that the yaw output is 0º when the vehicle (x-axis of the MTi) is
pointing North, it is recommended to select NWU or NED as the reference coordinate system. In
section 4.11 the various alignment resets are described.
Note that for proper working of the MTi-G in the automotive filter profile, it is needed to mount the MTi
in such a way that the yaw indicates 0 deg in the direction of the vehicle. For ENU coordinate systems
without an alignment reset, this means that the y-axis of the MTi-G should point to the front of the
vehicle, in NWU and NED coordinate systems that means that the x-axis of the MTi-G should point to
the front of the vehicle.
4
IEEE Standard for Inertial Systems Terminology
