LEA-6 / NEO-6 / MAX-6 - Hardware Integration Manual
UBX-14054794
Production Information
Appendix
Page 81 of 85
D
DR calibration
D.1
Constraints
The calibration of the DR sensors is a transparent and continuously ongoing process during periods of good GPS
reception:
Gyroscope Bias
Voltage level of the gyroscope while driving a straight route or not
moving
Gyroscope Scale Factor
Adjusted while in left and right turns; gyro sensitivity
Speed Pulse Scale Factor
Used to calibrate odometer pulse frequency to GPS speed over ground
Temperature Compensation
The gyroscope is a temperature-dependent device that requires
temperature compensation
When a new GPS receiver is installed in a vehicle, the accuracy is only
moderately
good
until sufficient
calibration
data has been collected, e.g. during a first drive. With time, continuous calibration results in
continuous improvement of dead reckoning accuracy. Small discontinuities, like deviating wheel diameters after
exchanging tires (summer vs. snow tires) or aging of the sensors, will be balanced out by ongoing automatic
calibration.
Calibration parameters must be
reset
, if
a DR module is transferred to a
different vehicle
and/or a
different gyroscope
is connected
the sensor integrity check has reported any failure from the sensors and set itself into
GPS only mode
Calibration can be reset with UBX message UBX – CFG (Config) – EKF (Extended Kalman Filter).
D.2
Initial calibration drive
For
optimum navigation performance
the system needs some learning time and distance for calibrating the
various sensors inputs. The following driving directions are recommended to achieve an efficient calibration so
dead reckoning yields high accuracy after the shortest possible period of time.
P
60
Find a place with open sky view
e.g. a big parking site
Start GPS and stand still for 90
seconds until valid position is
calculated
Drive straight route for 500m, at
least 40 km/h
Drive curves and straight segments
for ca. 5 minutes with good
visibility in any order
Exeed 60 km/h for at least 10 sec
Make at least two sharp left turns
(90 deg or more)
Make at least two sharp right turns
(90 deg or more)
Collect data of active temperature
compensation
Phase I
Phase II
Phase III
Phase IV
In
iti
a
l C
a
lib
ra
tio
n
O
n
g
o
in
g
F
in
e
C
a
lib
ra
tio
n
Figure 70: Initial DR Calibration Drive
The mentioned distances and durations are typical values, a better indication is the sensor calibration status
given in UBX – ESF (External Sensor Fusion) – STATUS (Status). The status values indicate which phase of the
initial calibration the receiver is in (calibrating, coarse calibration, fine calibration). In
Phase IV
good DR
