ROS: Reading GPS Data

This function reads GPS module data through the terminal and parses the GPS data to obtain latitude, longitude, and altitude data.

1. Reading GPS Data Through the Terminal

In the terminal, enter,

ros2 launch nmea_navsat_driver nmea_serial_driver.launch.py

Then let's check the topic data. In the terminal, enter,

ros2 topic list

Here is a description of the data of these GPS topics,

Topic	Type	Description
/extend_fix	gps_common/GPSFix	The GPSFix message contains the GPS satellite status and positioning information
/fix	sensor_msgs/NavSatFix	GPS positioning information
/time_reference	sensor_msgs/TimeReferencd	GPS time information
/vel	geometry_msgs/TwistStamped	GPS speed information

For the message types of each topic, refer to the official website URLs below,

sensor_msgs/NavSatFix Documentation (ros.org)

sensor_msgs/TimeReference Documentation (ros.org)

geometry_msgs/TwistStamped Documentation (ros.org)

We can print these topic messages in the terminal, and what we get is the GPS data. Taking printing /fix as an example, enter in the terminal

ros2 topic echo /fix

The terminal will print the following data,

Here, latitude, longitude, and altitude represent the latitude, longitude, and altitude respectively.

2. Reading the Latitude, Longitude, and Altitude of the GPS Data

Run in the terminal,

ros2 launch nmea_navsat_driver nmea_serial_driver.launch.py

In another terminal, run,

ros2 run nmea_navsat_driver read_lat_long.py

The data printed in the terminal is the current latitude, longitude, and altitude of the GPS module. Let's look at the source code, read_lat_long.py

#! /usr/bin/env python3
# -*- coding: utf-8 -*-
import rclpy
from rclpy.node import Node
from sensor_msgs.msg import NavSatFix

class GPSSubscriber(Node):
    def __init__(self):
        super().__init__('GPS_subscriber')
        self.subscription = self.create_subscription(
            NavSatFix,
            '/fix',
            self.gps_callback,
            10)
        self.subscription

    def gps_callback(self, msg):
        self.get_logger().info(f"latitude:{msg.latitude:.6f}, longitude:{msg.longitude:.6f}, altitude:{msg.altitude:.6f}")

def main(args=None):
    rclpy.init(args=args)
    gps_subscriber = GPSSubscriber()
    rclpy.spin(gps_subscriber)
    gps_subscriber.destroy_node()
    rclpy.shutdown()

if __name__ == '__main__':
    main()

The program subscribes to the data of the /fix topic, then performs parsing in the callback function, and finally prints to the terminal.

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