Operating Instructions and Installation Instructions

ComNav Vector G2/G2B Installation & Operation Operation

Document PN 29010078 V2.0 - 44 -

DRAFT #3 – 29 May 2009

Gyro-aided RTK

The Vector G2’s internal gyro offers several benefits. It will shorten reacquisition times

when the G2’s heading computation is stopped due to momentary obstruction of GPS

satellite signals, by reducing the search volume required for solution of the RTK, after

obstruction of the signals ends.

The gyro measures the relative angular change in the heading since the last valid RTK

heading was computed; in conjunction with the tilt sensor, it reduces the search volume

to a wedge-shaped location within the “tilt sensor ring” on the surface of the search

sphere.

Figure 18 – Tilt & Gyro-aided Search

An additional feature of the gyro is that it can provide an accurate substitute heading for a

short period (depending on the Roll and Pitch motions of the vessel), during instances of

momentary obstruction of GPS satellite signals at either antenna; this may occur, for

example, when passing close to high vertical walls, or underneath bridges.

When such obstructions occur, the gyro is automatically used to provide an alternate

source of heading, accurate to within 1°, for up to 3 minutes

. Ideally, the gyro-based

heading will see the system through to reacquisition.

If the outage lasts longer than 3 minutes, the gyro is deemed to have drifted too far and

the G2 will begin outputting NULL fields in the heading output sentences, which in turn

will typically cause a “lost heading” alarm on navigation devices.

Normal heading output will return automatically once satellite signals are re-acquired.

As well, the gyro helps improve and smooth (filter) the heading and rate of turn data

output by the G2; it is used to update the HTAU-smoothed (see page 59) heading output

from the RTK

computatio

n. This means that if the value of HTAU is increased while the

gyro is enabled, there will be little to no lag in heading output due to vessel manoeuvres.

The gyro will initialize itself at power-up and during initialization, or can be calibrated by

the user, as outlined the GPS Technical Reference manual.

L Caution! While the gyro is initializing, it is important that the

dynamics that the gyro experiences during its warm-up period are

similar to the vessel’s regular operating dynamics.

For example, if you will be using the G2 on a high speed,

manoeuvrable vessel, it is essential that the vessel is operating in

an environment of high dynamic movement – high speed, fast

turns, sudden jolts (e.g., over waves), vibration, etc. – for the first

5 to 10 minutes after the G2 is turned on, instead of sitting

stationary.

There is no user control over the gyro time-out period.