Global Navigation Satellite Systems (GNSS)
Achieve spot-on outdoor positioning for your autonomous mobile robots using GNSS. Tap into satellite networks like GPS, Galileo, and BeiDou so AGVs can handle tricky terrains with centimeter-level precision, making it easy to move between sites or tackle rough outdoor jobs.
_hero.png)
Core Concepts
Trilateration
The math robots use to pinpoint their location. They measure distances to at least four satellites to lock in their exact 3D coordinates.
RTK Correction
Real-Time Kinematic positioning wipes out errors using a fixed base station, boosting accuracy from meters to just 1-3 centimeters.
Multi-Constellation
Today's receivers track GPS, GLONASS, Galileo, and BeiDou all at once. This backup keeps signals coming even in city canyons or spotty coverage.
Sensor Fusion
GNSS rarely flies solo—it's combined with IMU and odometry data through Kalman filters to stay on track during signal dropouts.
Update Rate
Fast robotics demand quick updates (10Hz to 20Hz) to keep the position data super fresh and match the robot's real-time spot.
NMEA Protocol
The go-to format (NMEA) for sending GNSS strings like GPGGA straight to the robot's brain.
How It Works: Precision Positioning
GNSS works on 'Time of Flight' magic. Satellites beam down signals with send times and orbit info; the AGV receiver crunches the time gap to figure distances to each one.
For basic nav, three satellites give 2D position (lat/long), and a fourth adds height. But atmosphere can mess with signals, causing meters of error.
In robotics, RTK (Real-Time Kinematic) is the go-to. A fixed 'Base Station' spots satellite glitches and beams corrections to the 'Rover' (your robot) over radio or internet (NTRIP). This syncs the carrier wave phase for the centimeter precision needed for docking or lane tracking.
_diagram.png)
Real-World Applications
Precision Agriculture
Autonomous tractors and harvesters use GNSS with RTK to trace crop rows with < 2cm error, cutting damage and fine-tuning fertilizer over huge fields.
Port Logistics & Container Handling
Automated Straddle Carriers use GNSS to find and stack containers in vast outdoor yards where tracks or markers just won't cut it.
Last-Mile Delivery Robots
Sidewalk delivery rovers lean on multi-constellation GNSS for city nav, flipping to visual odometry under thick trees or skyscrapers.
Open-Pit Mining
Huge autonomous haul trucks run non-stop, 24/7, across mining sites, using GNSS to plan routes, dodge collisions, and dump loads with pinpoint accuracy.
Frequently Asked Questions
What is the difference between GPS and GNSS?
GPS is the US-owned satellite network. GNSS is the broader term covering GPS plus Europe's Galileo, Russia's GLONASS, and China's BeiDou. Modern robots use GNSS receivers to tap into all these satellites at once for superior accuracy and reliability.
Can GNSS be used for indoor autonomous robots?
Generally, no. Satellite signals are way too weak to get through roofs or thick walls—they just vanish. For indoor navigation, robots turn to LiDAR SLAM, visual SLAM, or setups like magnetic tape or QR codes.
What’s RTK, and does your AGV really need it?
RTK, or Real-Time Kinematic, boosts GNSS accuracy from meters down to centimeters. If your robot's cruising open spaces without super-tight tolerances (think drones), basic GNSS might do the trick. But for ground bots hugging sidewalks or docking precisely, RTK is a must.
How does a robot deal with 'urban canyons' or losing signal?
When skyscrapers block the satellites, robots switch to dead reckoning. They use onboard IMUs (like accelerometers and gyroscopes) plus wheel encoders to guess their position from the last good GNSS fix. This error builds up over time, though, so they need to grab a new signal fast.
What's the usual update rate for a robot's GNSS receiver?
Your phone's GPS refreshes at 1Hz—once a second. Robots often need 5Hz, 10Hz, or even 20Hz. Higher rates feed fresh position data to the control system, which is key for smooth tracking at speed.
Do I need my own base station for RTK?
Not always. Sure, you could set up your own base station, but lots of areas have NTRIP services ready to go. These stream correction data over cellular from a network of reference stations straight to your robot.
How does weather affect GNSS performance for robots?
GNSS laughs off most weather—rain, fog, snow, no problem—which beats cameras or LiDAR in tough conditions. Solar storms can mess with the ionosphere and hurt accuracy, but RTK steps in to fix those atmospheric glitches.
How expensive is a high-precision GNSS setup?
Prices have plummeted. Survey gear still runs thousands, but robotics-friendly dual-band RTK modules (like those based on u-blox F9P) go for just a few hundred bucks. Integration work and a solid antenna often eat up the real budget.
What’s dual-band GNSS (L1/L5 or L1/L2), and why bother?
Dual-band receivers tune into two satellite frequencies at the same time. This lets them correct ionospheric delays on the fly. For robots, it means quicker fixes and rock-solid signals even in tricky spots.
How is GNSS integrated into ROS (Robot Operating System)?
In ROS/ROS2, GNSS data flows through the `sensor_msgs/NavSatFix` message. Tools like `robot_localization` blend it with IMU and odometry data to keep a steady `map` to `base_link` transform, so the nav stack can plot global paths seamlessly.
What’s the 'multipath' effect, and how do robots fight it?
Multipath happens when signals bounce off buildings or the ground before reaching the antenna, tricking the receiver on distances. Robots counter with premium antennas (choke ring or helix types), mounting them high, and smart filtering in the receiver's software.
What are the power requirements for GNSS modules?
GNSS modules sip power—100mW to 500mW while tracking. That's nothing for big AGVs, but watch it on tiny battery-powered bots or sensors. The active antenna pulls a bit more through the bias tee.