How are GPS and IMU used for vehicle localization?

GPS (Global Positioning System) provides absolute position using satellite signals, achieving accuracy of 1-3 meters (or centimeters with RTK corrections). IMU (Inertial Measurement Unit) contains accelerometers and gyroscopes measuring vehicle motion without external references. Together, they enable localization: GPS provides position updates (typically 10 Hz), IMU provides high-frequency motion sensing (100+ Hz), and sensor fusion (often Kalman filter) combines them for continuous position estimation. GPS may be unavailable in tunnels or urban canyons, where IMU continues estimating position. Additional sensors (wheel odometry, cameras, lidar) enhance localization accuracy for autonomous driving.