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Document MT1600P.2019.A
© Xsens Technologies B.V.
MTi Family Reference Manual
Interpretation of yaw as heading
Heading is defined as the angle between the north direction and the horizontal projection of the roll axis.
Heading is positive about the local vertical axis following the right-hand rule
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.
With the default ENU L
XYZ
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 7 shows the different yaw values corresponding to the different local
coordinate systems that are available for the MTi.
Table 7: 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 (X axis of L
XYZ
). When it is required that the yaw output is 0º when the x-axis of the MTi is
pointing North, it is recommended to select NWU or NED as the local coordinate system. In section 0
the various alignment resets are described.
When using the INS/GNSS products in an automotive application, as a best practice pay proper attention
to mounting of the MTi on the automotive platform/vehicle. It is recommended to always mount the MTi
with the x-axis pointing to the front of the vehicle irrespective of the local coordinate frame used for the
output data.
True North vs. Magnetic North
As defined above, the output coordinate system of the MTi is with respect to local Magnetic North. The
deviation between Magnetic North and True North (known as the magnetic declination) varies depending
on the location on earth and can be roughly obtained from the latest World Magnetic Model
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of the
earth’s magnetic field as a fun
ction of latitude and longitude. The MTi accepts a setting of the declination
value. This is done by setting the position in the MT Manager, SDK or by Low level communication. The
yaw/heading will then be corrected for the declination calculated internally
and thus referenced to “local”
True North. The GNSS/INS products set automatically the current position when a GNSS-position fix is
available, therefore the user does not have to insert it.
4.2.4 Velocity data
Velocity data, calculated by the sensor fusion algorithm is provided in the same coordinate system as
the orientation data (L
XYZ
), and thus adopts orientation resets as well (if any is applied). The velocity
output is available in all GNSS/INS products (MTi-G-710, MTi-7 and MTi-670).
Note that the velocity data coming directly from the PVT (Position Velocity Time) data retrieved from any
GNSS receiver provided with any Xsens development kit is represented in the NED reference frame.
Different GNSS receivers may represent the velocity in different coordinate frames.
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IEEE Std 1559
TM
-2009: IEEE Standard for Inertial Systems Terminology
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Xsens releases a firmware update when a new WMM version is available