Hemisphere GPS Crescent V100 Series, User Manual

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Crescent V100 Series User Guide
51
Gyro Aiding
The Crescent V100’s internal gyro offers several benefits. It will
shorten reacquisition times when a GPS heading is lost due to
obstruction of satellite signals, by reducing the search volume
required for solution of the RTK. 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 2-3.)
Figure 2-3. Crescent V100’s gyro aiding
The gyro aiding accurately smooths the heading output and the
rate of turn. It will also provide 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 will
provide an alternate source of heading accurate to within 1
°
for up
to 3 minutes in times of GPS loss for either antenna. If the outage
lasts longer than three minutes, the gyro will be deemed to have
drifted too far and the Crescent V100 will begin outputting null
fields in the heading output messages. There is no user control
over the time-out period of the gyro.
The gyro will initialize itself at power-up and during initialization, or
can be calibrated by the user as outlined in Hemisphere GPS’ GPS
Technical Reference manual. 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