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If the RT is mounted in the vehicle with a large heading offset then the initial value
of heading will be incorrect. This can also happen if the RT is initialised in a turn.
This can lead to problems later.
4. When the combined accuracy of heading plus the orientation accuracy figure for
the secondary antenna is sufficiently accurate then the RT will solve the RTK
Integer problem using the inertial heading. There is no need for the RT to solve the
RTK Integer problem by searching.
If the antenna angle is offset from the RT by a lot then the RTK Integer solution
that is solved will be incorrect. For a 2 m antenna separation the RT orientation
and the secondary antenna orientation should be known to within 5°. For wider
separations the secondary antenna orientation angle needs to be more accurate.
5. Once the RTK Integer solution is available, the RT can start to use the dual antenna
solution to improve heading. The level of correction that can be applied depends
on how accurately the angle of the secondary antenna is known compared to the
inertial sensors.
6. The Kalman filter tries to estimate the angle between the inertial sensors and the
secondary antenna. The default value used in the configuration software (5°) is not
accurate enough so that the RT can improve the heading using this value. If you
want the vehicle heading to 0.1°, but the angle of the two GNSS antennas is only
known to 5°, then the measurements from the antenna are not going to be able to
improve the heading of the vehicle.
Driving a normal warm-up, with stops, starts and turns, helps the Kalman filter
improve the accuracy of the secondary antenna angle. The accuracy of this angle
is available in the verified in NAVdisplay.
7. In the unlikely event that the RTK Integer solution is incorrect at the start then the
Kalman filter can update the secondary antenna orientation incorrectly. If this
happens then things start to go wrong. The Kalman filter becomes more convinced
that it is correct, so it resolves faster, but it always solves incorrectly. Solving
incorrectly makes the situation worse.
To avoid the Kalman filter from getting things wrong it is possible to drive a
calibration run, then use the Get settings utility within NAVconfig (see page 59
for more information). This tells the Kalman filter it has already estimated the angle
of the secondary antenna in the past and it will be much less likely to get it wrong
or change it. This step should only be done if the RT is permanently mounted in a
vehicle and the antennas are bolted on. Any movement of either the RT or the
antennas will upset the algorithms.
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