Hemisphere GPS V102 G, User Manual

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V102 GPS Compass User Guide
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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: V102’s gyro aiding
The gyro aiding accurately smoothes the heading output and the rate of
turn. It provides an accurate substitute heading for a short period depending
on the roll and pitch of the vessel, ideally seeing the system through to
reacquisition. The gyro provides an alternate source of heading, 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 V102 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 powerup and during initialization, or you can
calibrate it as outlined in Hemisphere GPS’ GPS Technical Reference. When
the gyro is first initializing, it is important that the dynamics that the gyro
experiences during this warmup period are similar to the regular operating
dynamics. For example, if you use the V102 on a high speed, maneuverable
craft, it is essential that when gyro aiding in the V102 is first turned on, use it