Document MT0605P.E
© Xsens Technologies B.V.
MTi User Manual
25
4.2 Coordinate systems
Data from the MTi is represented in various coordinate systems, which are explained below.
4.2.1
Calibrated inertial data and magnetic field data
The
sensor coordinate system (S)
is a right-handed coordinate Carthesian system that is body-fixed
to the device and is used to output rate-of-turn (DataID 0x8020), acceleration (DataID 0x4020) and
magnetic field (DataID 0xC020). The encased version of the MTi shows the coordinate system on the
sticker. Depicted below is the sensor coordinate system on the encased MTi and the OEM version.
Small x, y and z are used for
(S)
and the object coordinate system
(O)
. Capital X, Y and Z are
generally
, but not always, used for velocity. They stand for the local-earth fixed coordinate system
(L)
,
see section 4.2.3.
The aluminum base plate of the MTi is carefully aligned with the output coordinate system during the
individual factory calibration. The alignment of the bottom plane and sides of the aluminum base-plate
with respect to the sensor-fixed output coordinate system (
S
) is within 0.1 deg. Convenient alignment
points are designed in the base plate of the MTi.
The non-orthogonality between the axes of the body-fixed co-ordinate system,
(S)
, is <0.05
. This also
means that the output of 3D linear acceleration, 3D rate of turn (gyro) and 3D magnetic field data all
will have orthogonal xyz readings within <0.05
as defined in the figure above.
It is possible to rotate the sensor coordinate system to an
object coordinate system (O)
when the
MTi is not exactly aligned with the axes of the object or vehicle the MTi is attached to. When this
alignment matrix has been applied, calibrated inertial data and magnetic field data are outputted in
(O)
. See section 4.11 for more information on alignment matrices.
4.2.2
Delta_angle and delta_velocity
The SDI output of the MTi contain delta_angle (dq, DataID 0x8030) and delta_velocity (dv, DataID
0x4010). These values represent the orientation change and velocity change during a certain interval.
In the MTi, this interval is 2.5 ms (400 Hz) by default. The values dq and dv are always represented in
the same coordinate system as calibrated inertial data and magnetic field data (see section 4.2.1),
which can be (S) or (O).
z
x
y
z
x
y
Figure 3: coordinate system of the encased MTi
(Note: origin is located at the accelerometers)
Figure 4: Coordinate system of the MTi-OEM
(Note: origin is located at the accelerometers)
