Applanix POS MV V5 Installation And Operation Manual page 242

POS MV V5 Installation and Operation Guide
Theory
of Operation
The magnitude of Schuler oscillations in the inertial navigator depends on the quality of platform
alignment. Similarly, the rate at which the position error grows depends partly on the quality of alignment
and partly on the magnitude of gyro bias.
To accomplish in-motion alignment the simple low-pass filter shown in Figure 97 on page B-31 is a more
sophisticated filter that has built into it a mathematical model. This mathematical model includes details of
the relationship between the quality of INS alignment, the gyro and accelerometer errors, and the
respective magnitudes of the Schuler oscillations and position error growth.
Such a filter is an algorithm that combines the operations of filtering and estimation. Its main function is to
estimate the internal dynamics of a system using measurements of the system outputs.
POS MV uses this 'Kalman' filter with the INS-GNSS position difference to estimate the position error, and
the cause of the INS position error (i.e. the alignment errors and the inertial sensor errors).
• The INS uses the estimated alignment error to correct and therefore improve the alignment of the
INS.
• The INS uses the estimated errors in the inertial sensors to correct and calibrate the outputs from
the inertial sensors.
This process does not require the INS platform (and therefore the vessel) to be stationary. In fact,
movements of the vessel actually assist the calibration process and provide a faster and more accurate
inertial sensor calibration.
B-32
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