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Document MT0605P.2018.E
© Xsens Technologies B.V.
MTi User Manual
The 3D orientation output (DataID 0x2010, 0x2020, 0x2030) is defined as the orientation between the
body-fixed co-ordinate system,
(S)
or
(O)
, and the earth-fixed co-ordinate system,
(L).
Orientation output modes
The output orientation can be presented in different parameterizations:
Unit Quaternions
Euler angles
2
: roll, pitch, yaw (XYZ Earth fixed type) are output following the aerospace
sequence (Z-Y’-X”)
Rotation Matrix (directional cosine matrix)
A positive rotation is always “right-handed”, i.e. defined according to the right hand rule (corkscrew rule).
This means a positive rotation is defined as clockwise in the direction of the axis of rotation.
Refer to
https://base.xsens.com/hc/en-us/articles/115004491045
to find more information on how
quaternions, Euler angles and the rotation matrix relate to each other.
Interpretation of yaw as heading
Heading is defined as the angle between north and horizontal projection of the vehicle roll axis. Heading
is positive about the local vertical axis following the right hand rule. For a local level navigation frame,
yaw is the angle from a horizontal navigation axis to the projection of the longitudinal axis in the
horizontal plane; positive is about the positive vertical axis following the right-handrule
3
.
With the default ENU
(L)
coordinate system, Xsens yaw output is defined as the angle between East
(X) and the horizontal projection of the sensor roll axis (x), positive about the local vertical axis (Z)
following the right hand rule. Table 6 shows the different yaw values corresponding to the different local
coordinate systems that are available for the MTi.
Table 6: Yaw in different coordinate systems (applies only to VRU/AHRS and GNSS/INS product types). The
MTi is assumed to be mounted with its roll-axis (X) aligned with the roll-axis of the vehicle (front of the
vehicle).
Local
coordinate
system (output)
Roll-axis of the vehicle
Yaw value
East-North-Up (ENU)
Pointing North
90 deg
East-North-Up (ENU)
Pointing East
0 deg
North-West-Up (NWU)
Pointing North
0 deg
North-East-Down (NED)
Pointing North
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 local coordinate system. In section 5.9 the
various alignment resets are described.
2
Please note that due to the definition of Euler angles there is a mathematical singularity when the sensor-fixed x-
axis is pointing up or down in the earth-fixed reference frame (i.e. pitch approaches ±90
). In practice this means
roll and pitch is not defined as such when pitch is close to ±90 deg. This singularity is in
no way
present in the
quaternion or rotation matrix output mode.
3
IEEE Std 1559
TM
-2009: IEEE Standard for Inertial Systems Terminology
