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Inertial Explorer
Chapter 1
Static coarse + fine alignment
Use this option if the IMU is static for longer than 120
seconds.
 Many high precision IMU applications recommend
approximately 2 minutes of coarse alignment
followed by 8 to 10 minutes of fine alignment.
Within 5 to 10 minutes, GNSS updates enable the
IMU to provide attitude information consistent with
the accuracy level achievable by the accelerometer/
gyro triad, with or without fine alignment. This
depends on the type of IMU, and the application’s
requirements. After roll, pitch and yaw are roughly
estimated for coarse alignment, fine alignment refines
them to a better level of precision.
Kinematic alignment
When neither static data or a priori attitude
information are available, alignment can be done
using vehicle motion. This requires a short period of
time where the vehicle is relatively level and moving
in a relatively straight line followed by some higher
dynamics, such as an aircraft S turn. The time period
can range from 4 to 40 seconds, depending on the
dynamics at the chosen start time.
This feature is useful when there is no static data.
While Inertial Explorer has been successful at
aligning tactical grade systems using this method,
there is no guarantee regarding lesser grade IMUs. It
might even be necessary to pick a different error
model in order to prevent instabilities arising in the
Kalman filter.
Transfer alignment
If roll, pitch and yaw are known, these values can be
entered as initial integration constants to allow
navigation to proceed. Attitude angles can be
provided by another IMU, in which case the
misalignment between the IMUs must be applied, or
they can be extracted from another trajectory, such as
the opposite processing direction.
Click Enter Attitude to enter initial attitude
information manually or select Get from Trajectory to
scan at a specified time from a defined IMU
trajectory.
The first epoch appearing in the IMU trajectory file of
the direction opposite that of the one being processed
is used. The attitude and velocities, as well as their
standard deviations, are loaded
Inertial Explorer 8.50 User Guide Rev 9
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