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Operation | HS80/MX575C/MX575D User Manual
This considerably decreases instances of incorrect headings as well as startup and
reacquisition times (see Figure 3-2).
Tilt angle
Figure 3-2: Smart GPS compass’s tilt aiding
Gyro aiding
The Smart GPS compass’s internal gyro offers several benefits. It reduces the sensor volume
for an RTK solution. This shortens reacquisition times when a GPS heading is lost because
the satellite signals were blocked. The gyro provides a relative change in angle since the last
computed heading, and, when used in conjunction with the tilt sensor, defines the search
space as a wedge-shaped location (see Figure 3-3).
Figure 3-3: Smart GPS compass’s gyro aiding
The gyro aiding accurately smooth the heading output and the rate of turn. It provides a
substitute heading for a short period, accurate to within 1º per minute for up to three
minutes, in times of GPS loss for either antenna. If the outage lasts longer than three minutes,
the gyro will have drifted too far and the Smart GPS compass begins outputting null fields in
the heading output messages. There is no user control over the timeout period of the gyro.
Calibration, which is set at the factory, is required for the gyro to remove latency from the
heading solution as well as provide backup heading when GPS is blocked. The receiver
will calibrate itself after running for a while but it may be important to follow the manual
calibration instructions if you want to guarantee performance quickly after powering up the
receiver.
The gyro initializes itself at power up and during initialization. There is no need for manual
calibration. When the gyro is first initializing, it is important that the dynamics that the
gyro experiences during this warm up period are similar to the regular operating dynamics.
For example, if you use the Smart GPS compass on a high speed, maneuverable craft, it is
recommended that when gyro aiding in the Smart GPS compass is first turned on, use it in
an environment that has high dynamics for the first five to ten minutes instead of sitting
stationary.
With the gyro enabled, the gyro is also used to update the post HTAU smoothed heading
output from the moving base station RTK GPS heading computation. This means that if the
HTAU value is increased while gyro aiding is enabled, there will be little to no lag in heading
output due to vehicle maneuvers.
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