ROSBridge and ROSLIBJS

Overview of ROSBridge and ROSLIBJS

This FAQ is deigned to provide an overview of ROSBridge and ROSLIBJS, two important tools for integrating web applications, such as the command control dashboard, with the Robot Operating System (ROS).

Table of contents

• What are ROSBridge and ROSLIBJS?

• How do ROSBridge and ROSLIBJS work together?

• How do I install and use ROSBridge and ROSLIBJS?

• Are there any limitations or challenges when using ROSBridge and ROSLIBJS?

What are ROSBridge and ROSLIBJS?

ROSBridge is a package for the Robot Operating System (ROS) that provides a JSON-based interface for interacting with ROS through WebSocket protocol (usually through TCP). It allows external applications to communicate with ROS over the web without using the native ROS communication protocol, making it easier to create web-based interfaces for ROS-based robots.

ROSLIBJS is a JavaScript library that enables web applications to communicate with ROSBridge, providing a simple API for interacting with ROS. It allows developers to write web applications that can send and receive messages, subscribe to topics, and call ROS services over websockets.

How do ROSBridge and ROSLIBJS work together?

ROSBridge acts as a bridge between the web application and the ROS system. It listens for incoming WebSocket connections and translates JSON messages to ROS messages, and the other way around. ROSLIBJS, on the other hand, provides an API for web applications to interact with ROSBridge, making it easy to send and receive ROS messages, subscribe to topics, and call services.

In a typical application utilizing ROSBridge and ROSLIBJS, it would have the following flow:

1. Web client uses ROSLIBJS to establish a WebSocket connection to the ROSBridge server, through specifying a specific IP address and port number.

2. The web client sends JSON messages to ROSBridge, which converts them to ROS messages and forwards them to the appropriate ROS nodes.

3. If the node has a reply, the ROS nodes send messages back to ROSBridge, which converts them to JSON and sends them over the WebSocket connection to the web client.

4. ROSLIBJS API processes the incoming JSON messages so it can be displayed/utilized to the web client

How do I install and use ROSBridge and ROSLIBJS?

ROSBridge Installation

The following assumes that you have ROS Noetic installed on your system.

To install ROSBridge you need to install the rosbridge-server package

sudo apt install ros-noetic-rosbridge-server

ROSLIBJS Installation

You can either use the hosted version of ROSLIBJS or download it for use in your project. To use the hosted version, include the following script tag in your HTML file:

<script src="https://static.robotwebtools.org/roslibjs/current/roslib.min.js"></script>

To download ROSLIBJS, visit the Github repository builds and download and save the files. To use the local version, include the following script tag in your HTML file:

<script src="PATH-TO-DOWNLOADED-SCRIPT"></script>

Simple Example

The following example is for React Application

First, download the roslib.min.js file from the ROSLIBJS GitHub repository and place it in your project's public directory.

Next, create a new React component called RosConnect:

RosConnect.jsx

import React, { Component } from 'react';
import { Alert } from 'react-bootstrap';

class ROSConnect extends Component {

    constructor() {
        super()
        this.state = { connected: false, ros: null } 
        
    }
    // run the function as soon as the page renders
    componentDidMount() {
        this.init_connection()
    }

    // a function to connect to the robot using ROSLIBJS
    init_connection() {
        this.state.ros = new window.ROSLIB.Ros()
        this.state.ros.on("connection", () => {
            this.setState({connected: true})
        })

        this.state.ros.on("close", () => {
            this.setState({connected: false})
            // try to reconnect to rosbridge every 3 seconds
            setTimeout(() => {
                try{
                    // ip address of the rosbridge server and port
                    this.state.ros.connect('ws://127.0.0.1:9090')
                }catch (error) {
                    console.log("connection error:", error);
                }
            // if the robot disconnects try to reconnect every 3 seconds (1000 ms = 1 second)
            }, 3000); 
        })

        try{
            // connect to rosbridge using websocket 
            this.state.ros.connect('ws://127.0.0.1:9090')
        }catch (error) {
            console.log("connection error:", error);
        }

    }

    render() { 
        return (
            // a Alert component from react-bootstrap showing if the robot is connected or not
            <div>
                <Alert className='text-center m-3' variant={this.state.connected ? "success" : "danger"}>
                    {this.state.connected ? "Robot Connected" : "Robot Disconnected"}
                </Alert>
            </div>
        );
    }
}
 
export default ROSConnect;

This component can be rendered to any page, for example it can be used in the App.js component which already comes with creat-react-app

Challenges and Limitations of ROSBridge and ROSLIBJS

Even though ROSBridge and ROSLIBJS is has a lot of use cases from being able to view camera feed from a robot to getting its GPS data display on a dashboard, it does have some prominent limitations.

While working on the campus command control project, one of the issues that was encountered was lag. ROSLIBJS uses web socket, which is built on top of Transmission Control Protocol (TCP). While TCP is more reliable, it transfers data more slowly, which led to lag in robot controls and video feed. It is worth mentioning that ROSBridge does support User Datagram Protocol (UDP), which comes at a cost of reliability for speed, but ROSLIBJS current implementation does not support UDP.