Operation; Filter; Initialisation; Hot Start - Advanced Navigation Spatial OEM Reference Manual

7

Operation

7.1

Filter

Spatial contains a very sophisticated filter which it uses to fuse all it's sensors into a state
estimation. The filter is a set of custom algorithms that have similar principles to a kalman filter, but
operate differently. Spatial's custom filter makes decisions based upon context and history which
greatly improves performance and makes it more resilient to error sources than a standard kalman
filter.
Under rare conditions, when there are large errors present that Spatial's filter cannot compensate
for, it can become unstable. If Spatial's filter does become unstable a monitoring process will
immediately reset the filter to the last known good state. The filter initialised flag will remain reset
until the filter stabilises again. In real time control applications it is very important to monitor
Spatial's filter status, so that data can be ignored if a situation occurs causing the filter to reset.
7.2

Initialisation

When Spatial starts up, it assumes that it can be in any orientation. To determine it's orientation it
uses the accelerometers to detect the gravity vector. Whilst this is occurring, if there are random
accelerations present these can cause an incorrect orientation to be detected. To prevent this,
Spatial monitors the accelerometers and gyroscopes and restarts the orientation detection if there
are sudden movements. It is however still possible under some circumstances for it to miss
movements and start with a bad orientation. In this scenario Spatial will progressively correct the
orientation error over a period of several seconds.
After orientation detection, Spatial's filter takes several minutes to achieve it's full accuracy. It is
recommended to wait two minutes after power on for applications requiring high accuracy.
7.3

Hot Start

Spatial is the first GNSS/INS on the market with hot start functionality. This allows Spatial to start
inertial navigation within 500 milliseconds and obtain a GNSS fix in as little as 3 seconds. Spatial's
hot start is always on and fully automatic.
A next generation backup battery system within Spatial provides the hot start ability for more than
24 hours without power. When Spatial hot starts it assumes that it is in the same position it was
when it lost power and begins navigating from that position. The hot start also provides ephemeris,
almanac and time information to the GNSS receiver which allows it to achieve a fix far more quickly
than it otherwise would. When the GNSS achieves it's first fix, if this position deviates from the hot
start position, Spatial will jump to the new position without causing any side effects to the filter.
Whilst Spatial is without power it keeps track of the time accurately to within 1 second so that the
time is immediately valid on a hot start.
Spatial's hot start is of particular benefit to vehicle tracking and robotics applications. The primary
benefits are immunity and fast recovery from power failure as well as fast startup time.
7.4

Time

Spatial was designed to provide a highly accurate time reference. When a GNSS fix is available
Spatial OEM Reference Manual
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