Heading Source; Magnetic Heading; Velocity Heading; External Heading - Advanced Navigation Spatial OEM Reference Manual

Spatial's time is accurate to within 50 nanoseconds. When a GNSS fix is lost, Spatial's time
accuracy typically remains within 10 microseconds over extended time periods. When Spatial hot
starts the time accuracy is typically within 1 second immediately on startup and corrected to within
50 nanoseconds as soon as a GNSS fix is achieved. To synchronise with Spatial's high accuracy
time, both the packet protocol and a 1PPS line must be used.
7.5

Heading Source

There are three different heading sources available for Spatial. The heading source can be
selected using the filter options dialog in Spatial Manager or the Filter Options Packet. It is possible
to use multiple heading sources and this can often provide performance benefits.
7.5.1

Magnetic Heading

This is the default heading source and works well in the majority of cases. When using magnetic
heading, calibration is required every time Spatial's installation changes. The downside of magnetic
heading is that prolonged dynamic magnetic interference sources can cause heading errors.
7.5.2

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 2 metres/second with a GNSS fix. The benefits of velocity heading are that it is immune to
magnetic interference and no calibration is required when Spatial's installation changes.
7.5.3

External Heading

This can be used if there is some other way to derive heading that is external to Spatial. Examples
include dual antenna GNSS systems, north seeking gyroscopes, reference markers and SLAM
systems. The heading must be fed into Spatial using the External Heading Packet or through
NMEA into a GPIO pin.
7.6

Magnetics

Static magnetic interference is resolved through magnetic calibration and dynamic magnetic
interference is compensated by a filter algorithm but should be minimised where possible through
installation location. Please see section 6.4 for more information on magnetic interference. To
compensate for static magnetic interference, magnetic calibration should be performed any time
Spatial's installation changes.
Spatial contains a dynamic magnetic compensation filter that is able to mitigate the effects of short
term magnetic interference sources while in operation. For example if Spatial is installed in a car
and the car drives over a large piece of magnetised steel, this will be compensated for. Another
example is driving through a tunnel which is built from heavily reinforced concrete. It is important to
note that for Spatial's dynamic magnetic compensation filter to operate correctly, Spatial needs to
get a GNSS fix at least once every time it is moved more than 50km. Each time Spatial moves
more than 50km the new position is stored permanently and allows Spatial to update it's world
magnetic model values.
There are two types of magnetic calibration available, these are 2D calibration and 3D calibration.
Spatial OEM Reference Manual
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Version 2.7