External Heading; Magnetics; Data Anti Aliasing; Vehicle Profiles - Advanced Navigation Spatial FOG Dual Reference Manual

10.5.4

External Heading

External heading can be used if there is some other way to derive heading that is
external to Spatial FOG Dual. Examples include reference markers and SLAM systems.
The heading must be fed into Spatial FOG Dual using the External Heading Packet or
through NMEA into a GPIO pin.
10.6

Magnetics

Spatial FOG Dual uses magnetometers to detect changes in heading which allows the
north seeking algorithm to initialise faster if another heading source is not available. If
strong dynamic magnetic disturbances are present this will not effect the accuracy of
the heading but may cause the north seeking initialisation to take longer when GNSS
is not available.
10.7

Data Anti Aliasing

Internally Spatial FOG Dual's filters update at 1000 Hz. When Spatial FOG Dual outputs
data, most applications require the data at a much lower rate (typically < 100 Hz).
This causes a problem for time based data such as velocities and accelerations where
aliasing will occur at the lower rate. To prevent this problem, if the output rate is lower
than 1000 Hz, Spatial FOG Dual will low pass filter the values of the time dependent
data between packets to prevent aliasing. This is only the case when a packet is set up
to output at a certain rate. If the packet is simply requested no anti aliasing will occur.
Additionally there is no anti aliasing for non time dependent fields such as position.
10.8

Vehicle Profiles

Spatial FOG Dual supports a number of different vehicle profiles. These vehicle profiles
impose constraints upon the filter that can increase performance. If your application
matches one of the available vehicle profiles, it is recommended to select it for use in
the filter options dialogue in Spatial FOG Manager, see section 11.8.2. For a list of the
different vehicle profiles please see section 13.10.5.1. Please note that if the wrong
vehicle profile is selected it can cause a significant decrease in performance.
10.9

Odometer Pulse Length

For Spatial FOG Dual to use a wheel speed sensor or odometer input, it must know the
pulse length of the signal. The pulse length is the distance in metres between low to
high transitions of the signal. The odometer pulse length can either be entered
manually or automatically calibrated by Spatial FOG Dual. To enter the pulse length
manually, please use the odometer configuration dialogue in Spatial FOG Manager,
see section 11.8.7. To automatically calibrate the odometer pulse length please use
the procedure listed below in section 10.9.1. By default the odometer will
automatically calibrate itself.
Spatial FOG Dual Reference Manual
Page 43 of 138
Version 1.0
26/06/2015