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Oxford Technical Solutions
Initialisation process
Before the RT can start to output all the navigation measurements, it needs to initialise
itself. In order to initialise, the RT needs all the measurements listed in Table 26.
Table 26. Quantities required for initialisation
Quantity
Description
Time
Measured by internal GNSS.
Position
Measured by internal GNSS.
Velocity
Measured by internal GNSS.
Heading
Approximated to course over ground (with large error) when the vehicle moves. Dual
antenna models have the option for static initialisation which does not require any
movement.
Roll, pitch
Vehicle Level option: assumed zero with a large error.
Otherwise: estimated over first 40 s of motion with large error.
The system will start when it has estimates of all of these quantities. Course over ground
will be used as the initial heading when the system exceeds the value set as the
initialisation speed (default of 5 m/s), unless static initialisation has been selected. If the
system is mounted level in the vehicle, then the Vehicle Level option will enable the
system to start immediately. Otherwise the system takes about 40 s to find approximate
values for roll and pitch.
For the initialisation process to work correctly, the RT requires the user to tell it which
way it is mounted in the vehicle, otherwise the course over ground will not be close
enough to the heading.
Real-time outputs
During the initialisation process the system runs 1 s behind, allowing GNSS information
to be compared to information from the inertial sensors. After initialisation the system
has to catch-up from this 1 s lag. It takes 10 s to do this. During the first 10 s the system
cannot output data in real time, the delay decays to the specified latency linearly over this
10 s period.
The system turns the SDNav LED orange to show the outputs are not real-time. When the
system is running in real time this LED is green.
