"Technically ARKit is a Visual Inertial Odometry (VIO) system, with some simple 2D plane detection. VIO means that the software tracks your position in space (your 6dof pose) in real-time i.e. your pose is recalculated in-between every frame refresh on your display, about 30 or more times a second. These calculations are done twice, in parallel. Your pose is tracked via the Visual (camera) system, by matching a point in the real world to a pixel on the camera sensor each frame. Your pose is also tracked by the Inertial system (your accelerometer & gyroscope — together referred to as the Inertial Measurement Unit or IMU). The output of both of those systems are then combined via a Kalman Filter which determines which of the two systems is providing the best estimate of your “real” position (referred to as Ground Truth) and publishes that pose update via the ARKit SDK. Just like your odometer in your car tracks the distance the car has traveled, the VIO system tracks the distance that your iPhone has traveled in 6D space. 6D means 3D of xyz motion (translation), plus 3D of pitch/yaw/roll (rotation).