GPS

What is GPS?

GPS (Global Positioning System) is a satellite-based navigation system that allows a receiver to determine its precise location (latitude, longitude, altitude) anywhere on Earth. In robotics, GPS is a critical component for outdoor navigation, localization, and global path planning.

How GPS Works

A GPS receiver calculates its position by measuring the time it takes for signals to travel from multiple satellites. At least four satellites are needed to determine 3D position and time.

  • Satellites transmit their position and time
  • Receiver calculates distance to each satellite
  • Using trilateration, it determines its own location

Applications of GPS in Robotics

1. Outdoor Mobile Robots

Robots such as delivery bots, autonomous lawnmowers, and agricultural robots use GPS for path following and navigation in open environments.

2. UAVs and Drones

GPS is vital for aerial vehicles to maintain position, return to home, and follow pre-defined routes.

3. Autonomous Cars

GPS helps provide a global position estimate that is fused with other sensors like LiDAR, IMU, and cameras for full autonomy.

4. SLAM and Mapping

While GPS is not used directly in SLAM, it provides global reference points that can correct accumulated errors in mapping.

GPS Accuracy and Enhancements

Standard GPS accuracy is about 5–10 meters, but several techniques improve it:

  • DGPS (Differential GPS): Improves accuracy to sub-meter levels using ground reference stations.
  • RTK (Real-Time Kinematic): Offers centimeter-level accuracy by using carrier-phase measurements and correction data.
  • Sensor Fusion: Combines GPS with IMU or odometry for smoother and more reliable localization.

GPS in ROS (Robot Operating System)

In ROS, GPS data is typically published as a sensor_msgs/NavSatFix message. A few popular GPS drivers and nodes include:

  • nmea_navsat_driver: Converts NMEA sentences to ROS messages
  • ublox: Supports high-precision GPS modules (RTK, DGPS)
  • robot_localization: Fuses GPS with IMU and other data for smooth state estimation

Limitations of GPS in Robotics

  • Does not work well indoors or in tunnels (requires fallback systems)
  • Signal can be degraded by buildings, trees, and atmospheric conditions
  • Low update rate compared to onboard sensors (typically 1–10 Hz)

Conclusion

GPS is a powerful tool in robotic systems, especially for outdoor and long-range navigation. While it has limitations in terms of precision and coverage, combining GPS with other sensors enables robust and scalable robotic solutions in real-world environments.