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Document MT1600P.2019.A
© Xsens Technologies B.V.
MTi Family Reference Manual
4.2.5 Position data
Position data, calculated by the sensor fusion algorithm is represented in Latitude, Longitude and
Altitude as in the WGS84 datum. The position output is available in all GNSS/INS products (MTi-G-710,
MTi-7 and MTi-670).
It is possible to retrieve position data calculated by the sensor fusion algorithm in Earth Centered
–
Earth
Fixed (ECEF) format. See
MT Low Level Communication Protocol Documentation
for more information
.
4.3 Physical sensor model
This section explains the basics of the individual calibration parameters of each MTi.
The physical sensors inside the MTi (accelerometers, gyroscopes and magnetometers)
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are all
calibrated according to a physical model of the response of the sensors to various physical quantities,
e.g. temperature. The basic model is linear and according to the following relation:
𝒔 = 𝑲
𝑻
−1
(𝒖 − 𝒃
𝑻
)
During factory calibration, to each MTi has been assigned a unique gain matrix,
K
T
and the bias vector,
b
T
. This calibration data is used to relate the sampled digital voltages,
u
, from the sensors to the
respective physical quantity,
s
.
The gain matrix is split into a misalignment matrix,
A
, and a gain matrix,
G
. The misalignment specifies
the directions of the sensitive axes with respect to the ribs of the sensor-fixed coordinate system (S
xyz
)
housing. E.g. the first accelerometer misalignment matrix element
a
1,x
describes the sensitive direction
of the accelerometer on channel one. The three sensitive directions are used to form the misalignment
matrix:
𝑨 = [
𝑎
1,𝑥
𝑎
1,𝑦
𝑎
1,𝑧
𝑎
2,𝑥
𝑎
2,𝑦
𝑎
2,𝑧
𝑎
3,𝑥
𝑎
3,𝑦
𝑎
3,𝑧
]
𝑮 = [
𝐺
1
0
0
0
𝐺
2
0
0
0
𝐺
3
]
𝑲
𝑻
= [
𝐺
1
0
0
0
𝐺
2
0
0
0
𝐺
3
] [
𝑎
1,𝑥
𝑎
1,𝑦
𝑎
1,𝑧
𝑎
2,𝑥
𝑎
2,𝑦
𝑎
2,𝑧
𝑎
3,𝑥
𝑎
3,𝑦
𝑎
3,𝑧
] + 𝑶
With
O
representing higher order models, temperature modelling, g-sensitivity corrections, etc.
Each individual MTi is modeled for temperature dependence of both gain and bias for all sensors and
other effects. This modeling is not represented by the simple model in the above equations but is
implemented in the firmware with the temperature coefficient being determined individually for each MTi
device during the calibration process. The basic indicative parameters in the above model of your
individual MTi can be found in MT Manager (Device Settings dialog).
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The barometer and GNSS receiver do not require additional calibration.
