Operation; Filter; Initialisation; Orientation Initialisation - Advanced Navigation Spatial FOG Dual Reference Manual

10

Operation

10.1

Filter

Spatial FOG Dual contains a 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 FOG Dual's custom filter
makes decisions based upon context and history which greatly improves performance
and makes it more resilient to error sources than a typical kalman filter.
Under rare conditions, when there are large errors present that Spatial FOG Dual's
filter cannot compensate for, it can become unstable. If Spatial FOG Dual'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 FOG
Dual's filter status, so that data can be ignored if a situation occurs causing the filter
to reset.
10.2

Initialisation

There are four different levels of initialisation on Spatial FOG Dual. These are
orientation, navigation, heading and time. The initialisation can be monitored by
inspecting the status view in Spatial FOG Manager, see section 11.7.2.
After all four levels of initialisation, Spatial FOG Dual's filter takes several minutes to
achieve it's full accuracy. It is recommended to wait two minutes after initialisation for
applications requiring high accuracy.
10.2.1

Orientation Initialisation

Orientation initialisation occurs automatically upon power on and typically completes
within several seconds. Once orientation initialisation is complete, the roll, pitch and
angular velocity values will be valid.
When Spatial FOG Dual 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.
Spatial FOG Dual Reference Manual
Illustration 23: The
four initialisation
levels
Page 39 of 138
Version 1.0
26/06/2015