Introduction to Global Localization
Global localization is a fundamental process in self-driving cars that determines the vehicle's position and orientation (pose) in a global coordinate frame, essential for navigation and path planning. Unlike local odometry, which tracks relative motion, global methods provide absolute positioning, often using external references.
Key components include:
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GPS (Global Positioning System): Satellites transmit signals to receivers, allowing triangulation to estimate position with accuracy around 1-5 meters in open areas. However, GPS can degrade in urban canyons or tunnels due to signal blockage.
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IMU (Inertial Measurement Unit): Combines accelerometers and gyroscopes to measure linear acceleration and angular velocity, providing short-term pose estimates but suffering from drift over time.
In self-driving cars, these sensors address the limitations of each other: GPS for long-term accuracy and IMU for high-frequency updates during GPS outages.
For example, consider a vehicle navigating a city; GPS provides the rough global position, while IMU bridges gaps when entering a tunnel.
Basic pose can be represented as a transformation matrix: $$ T = \begin{bmatrix} R & t \ 0 & 1 \end{bmatrix} $$ where $R$ is the rotation matrix and $t$ is the translation vector.