POS MV V5 Installation and Operation Guide
Theory
of Operation
Copyright © Applanix Corporation, 2017
B-18
GNSS attitude sensors that have antenna separations of between one and three metres. They
will vary according to the multipath signal environment affecting the antennas.
Each of the above heading measurement methods have advantages and disadvantages:
•
An inertial navigator that undergoes dynamic heading alignment delivers heading measurements
that suffer from drift but are relatively unaffected by noise.
•
GAMS heading error is largely due to noise but exhibits no drift.
POS MV uses the advantages of each method to compensate for the disadvantages of the other. By
blending the measurements delivered by GAMS with those delivered by the inertial navigator, POS MV
averages the heading error over time and delivers blended measurements to an accuracy of between
0.02° and 0.1° RMS.
Heading Measurements
Heading measurements calculated by GAMS provide aiding data to the Kalman Filter to improve the
heading estimate made by the strap-down navigator.
Baselines
Heading measurements used by POS MV are:
•
The true heading of the vessel in a geographic navigation frame of reference
•
The ‘heading’ of the IMU in a geographic frame of reference
- that is, the geographic heading of
the
x-axis
of the IMU body frame
To deliver heading measurements of the required accuracy, POS MV blends measurements made by
GAMS and measurements made by the inertial navigator. A Kalman Filter performs this blending
operation.
POS MV includes a primary and a secondary GNSS receiver, each with its own antenna. The GNSS
System topic on page 2-5 of this manual includes instructions to install both GNSS antennas so that they
are rigid relative to each other and relative to the IMU, and are separated by a distance of between one
and five metres.
By using a carrier phase differential GNSS algorithm, POS MV can measure the vector between the two
antennas in a geographic frame of reference. Figure 89 illustrates this situation. The Carrier Phase
Differential Position topic on page B-22 explains the process of carrier phase differential GNSS
measurement.