Spatial FOG Reference Manual
Page 46 of 144
Version 2.3
03/05/2018
10.5
Magnetics
Spatial FOG uses magnetometers to detect changes in heading which allows the north
seeking algorithm to initialise faster. If strong dynamic magnetic disturbances are
present this will not efect the accuracy of the heading but may cause the north
seeking initialisation to take longer.
10.6
Data Anti Aliasing
Internally Spatial FOG's filters update at 1000 Hz. When Spatial FOG 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 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.
10.7
Vehicle Profiles
Spatial FOG supports a number of diferent 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
diferent 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.
10.8
Odometer Pulse Length
For Spatial FOG 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. 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 10.8.1. By default the odometer will
automatically calibrate itself.
10.8.1
Odometer Automatic Pulse Length Calibration Procedure
1. Ensure that the signal is connected correctly and that the GPIO pin is configured
as an odometer input using the GPIO configuration dialogue in Spatial FOG
Manager, see section 11.8.6.
2. Open Spatial FOG Manager, connect to Spatial FOG and open the odometer
configuration dialogue. In the odometer configuration dialogue tick the
automatic pulse length calibration check box and press the write button, see
section 11.8.7.
3. Wait until Spatial FOG has a continuous GNSS fix and then drive 1000 metres
over fat terrain with as little turning as possible.
