Velocity Heading - Advanced Navigation Spatial FOG Dual Reference Manual

velocity heading, the north seeking algorithm will automatically initialise during the
first 60 seconds of operation without any intervention required.
When used as the sole heading source, the north seeking initialisation procedure is:
1. Turn on Spatial FOG Dual and leave stationary for 5 minutes.
2. Rotate Spatial FOG Dual approximately +90 degrees about the Z axis and leave
stationary for 3 minutes.
3. Rotate Spatial FOG Dual approximately +90 degrees about the Z axis and leave
stationary for 3 minutes.
4. Rotate Spatial FOG Dual approximately +90 degrees about the Z axis and leave
stationary for 3 minutes.
To assist users in getting accustomed to the north seeking procedure there is a north
seeking status dialogue in Spatial FOG Manager that provides feedback and guides the
user through the initialisation process, see section 11.7.12.
Spatial FOG Dual's gyrocompass heading is fully automatic and always on. For all
applications, the gyrocompass heading requires approximate position. For moving
applications, the gyrocompass heading function requires continuous velocity updates
to provide accurate heading. This data is typically provided by the internal GNSS
receiver, however it can also be provided by an odometer or other type of speed
sensor.
Applications where north seeking should not be used as the sole heading source
include
Environments with high vibration.
•
Environments with rapid temperature fluctuations.
•
Environments with strong changing magnetic fields close to the FOG unit (the
•
fibre optic gyroscopes bias is affected by strong magnetic fields).
Applications where it is impractical to perform the initialisation procedure.
•
Applications where the system is moving at speeds of over 1 metre/second and
•
no velocity aiding information is available.
In these scenarios an alternative heading source should be considered. Please see the
alternative options of Dual Antenna Heading, Velocity Heading and External Heading. If
in doubt, please contact Advanced Navigation support for assistance in selecting the
correct heading source for your application.
10.5.3

Velocity Heading

Velocity heading works by deriving heading from the direction of velocity and
acceleration. Velocity heading works well with cars, boats, fixed wing aircraft and other
vehicles that don't move sideways. Velocity heading does not work with helicopters
and other 3D vehicles. The downside of velocity heading is that heading can not be
measured until the vehicle moves at a horizontal speed of over 1.15 metres/second
with a GNSS fix. Velocity heading is very useful for getting accurate heading quickly on
moving vehicles without requiring any specific initialisation procedure.
Spatial FOG Dual Reference Manual
Page 42 of 138
Version 1.0
26/06/2015