Sep 09, 2019

Initial calibration of the **inertial navigation system** is required. Generally, a reference navigation system (such as GNSS) is used to give the inertial navigation system an initial position value (the purpose is to establish an initial coordinate transformation matrix of the geographic coordinate system and the earth coordinate system) and an initial velocity value; the measured value by the IMU itself or by means of a measuring instrument (inclinometer or dual-antenna high-precision GPS orientation system) obtains the initial attitude angle (the IMU outputs the attitude angle of the carrier coordinate system relative to the local horizontal navigation coordinate system, also called the Euler angle), and the quaternion and coordinate transformation matrix Initialize.

For the indoor positioning system, a custom local rectangular coordinate system (generally select a certain angle of the positioning area as the origin, the boundary line as the x-axis, the right-hand criterion to determine the y-axis, and the vertical ground as the z-axis) as the navigation coordinate system. Since both are Cartesian coordinates but the origin and direction of the coordinate system are different, the origin displacement and the coordinate axis rotation are required, so initial alignment is also required.

After the initial alignment is completed, the inertial navigation calculation process is entered, and the angular velocity measurement value of the IMU is read to update the quaternion and the attitude transformation matrix, thereby updating the speed and position, and finally, the velocity and position can be converted to other target coordinate systems for expression. For example, the latitude and longitude high earth coordinate system of GNSS.

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