PyQt and ROS2 Message Interface

PyQt is a set of Python bindings for the Qt application framework and runs on all platforms supported by Qt including Windows, OS X, Linux, iOS, and Android. ROS2 (Robot Operating System 2) is a set of software libraries and tools for building robot applications. In this article, we will explore how to create a message interface between PyQt and ROS2.

Topic and Service

In ROS2, messages are exchanged between different nodes using topics and services. Topics are used for asynchronous communication and can have multiple publishers and subscribers. Services, on the other hand, are used for synchronous communication and allow clients to request a specific service from a server.

Creating a Message Interface

To create a message interface between PyQt and ROS2, we can use the rclpy package provided by ROS2 and the PyQt5 package for building the user interface. First, we need to install the necessary packages using pip:

    
      $ pip install pyqt5
      $ pip install rclpy
    
  

Next, we can create a ROS2 node in Python using rclpy to publish and subscribe to messages. We can define the message structure using ROS2 message types such as std_msgs/String or custom message types. Then, we can create a PyQt application that provides a user interface for interacting with the ROS2 node. We can use PyQt widgets to display messages received from the ROS2 node and to send messages to the ROS2 node.

Example

Here is an example of a simple PyQt application that publishes and subscribes to a custom message type “CustomMsg” using ROS2:

    
import sys
import rclpy
from custom_msgs.msg import CustomMsg
from PyQt5.QtWidgets import QApplication, QLabel, QPushButton, QVBoxLayout, QWidget

class Ros2PyQtApp(QWidget):
    def __init__(self, node):
        super().__init__()
        self.node = node
        self.subscriber = self.node.create_subscription(CustomMsg, 'custom_msg', self.custom_msg_callback, 10)
        self.publisher = self.node.create_publisher(CustomMsg, 'custom_msg')

        self.setLayout(QVBoxLayout())
        self.label = QLabel("Received Message: ")
        self.layout().addWidget(self.label)
        self.button = QPushButton("Send Message")
        self.button.clicked.connect(self.send_custom_msg)
        self.layout().addWidget(self.button)

    def custom_msg_callback(self, msg):
        self.label.setText(f"Received Message: {msg.message}")

    def send_custom_msg(self):
        msg = CustomMsg()
        msg.message = "Hello, ROS2!"
        self.publisher.publish(msg)

def main():
    rclpy.init()
    node = rclpy.create_node('ros2_pyqt_app')
    app = QApplication(sys.argv)
    widget = Ros2PyQtApp(node)
    widget.show()
    sys.exit(app.exec_())

if __name__ == '__main__':
    main()
    
  

Conclusion

In this article, we have seen how to create a message interface between PyQt and ROS2 using Python. By integrating the user interface capabilities of PyQt with the message passing capabilities of ROS2, we can build powerful applications for controlling and monitoring robot systems.