What is an IMU?
An IMU, or inertial measurement unit, is a sensor that tracks how something is moving and which way it's facing. It typically combines an accelerometer to detect acceleration, a gyroscope to detect rotation, and sometimes a magnetometer to detect heading, like a compass, building a full picture of an object's motion and orientation in real time.
How do IMUs work?
Modern IMUs combine multiple microelectromechanical (MEMS) sensors to track an object's movement and orientation. Accelerometers measure linear acceleration along three axes, while gyroscopes measure rotational movement. Some IMUs also include magnetometers, which use Earth's magnetic field to provide an additional reference for orientation.
Combining these sensors helps compensate for the limitations of each one individually. Accelerometer-based position estimates can accumulate error over time, while gyroscopes provide responsive rotational tracking but can experience orientation drift. Sensor fusion combines their measurements to produce a more stable estimate of movement and orientation.
In VR and AR, IMU data is used to track head and device movement with low latency, helping virtual environments respond naturally as users move. Development platforms can combine IMU data with complementary tracking methods, such as cameras and optical positioning, to achieve precise 6DOF (six-degrees-of-freedom) tracking that accounts for both rotation and position in space.
The quality and capabilities of an IMU vary between devices. Standalone VR headsets typically use dedicated IMUs designed for responsive, low-drift tracking, while smartphone-based XR experiences rely on built-in sensors that can differ in accuracy, sampling rate, and capabilities. These differences are important when developing cross-platform applications that need consistent tracking across different hardware.