An Inertial Measurement Unit (IMU) is a device that measures the three-axis attitude angles (or angular rates) and acceleration of an object. Typically, an IMU consists of three single-axis accelerometers and three single-axis gyroscopes. The accelerometers detect the acceleration signals of the object along the three independent axes of the carrier coordinate system, while the gyroscopes detect the angular velocity signals of the carrier relative to the navigation coordinate system, thereby measuring the angular velocity and acceleration of the object in three-dimensional space.
An Attitude and Heading Reference System (AHRS) includes MEMS-based three-axis gyroscopes, accelerometers, and magnetometers. Unlike an IMU, which measures attitude relative to its own initial attitude, an AHRS determines its own attitude by referencing the Earth.
VRU stands for Vertical Reference Unit (also known as a vertical gyro). It shares the same hardware structure as an IMU. By using the Kalman filter algorithm, the VRU not only outputs the data provided by an IMU but also adds pitch and roll angle outputs. Some VRUs also output relative azimuth angles, which are also referred to as Euler angle outputs. The performance achievable by a VRU is highly dependent on the algorithmic capabilities of the engineer.
GNSS (Global Navigation Satellite System) is a global satellite navigation system, which includes GPS (United States), GLONASS (Russia’s Global Navigation Satellite System), and BDS (BeiDou Navigation Satellite System).
The full name of INS is Inertial Navigation System. While an IMU is a device that measures angular velocity and acceleration, an INS can determine the motion of a moving carrier in the inertial reference coordinate system using the measured angular velocity and acceleration values.
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