Documentation for lidar-firebase(Client-Server Communication)

This is part of the LiDAR Data Streaming Project developed at TiHAN, IIT-H

This is an alternative to using WebRTC; when either of the devices are behind Symmetric NAT (AKA Full-Cone NAT). The type of NAT can be checked here. Permissive NAT is a requirement for Peer-to-Peer (WebRTC) communication.

To learn more about NAT, go here.

NOTE: A TURN Server is often cheaper than this method, however, it only allows single subscriber of the data stream. In contrast, this method allows multiple subscribers.

Environment Setup

ROS (preferably melodic version for Ubuntu 18.04) is required to be setup on both the sender (encoder) and the receiver (decoder).

ROS-Bridge Server Setup

ROS-Bridge server needs to be installed for roslibjs which was part of the project that this repository was intended for.

Installation: (Change melodic to the required version)

sudo apt-get install ros-melodic-rosbridge-server

Starting Server:

roslaunch rosbridge_server rosbridge_websocket.launch

Node Package Manager (NPM) and Node.js are required to be installed (npm@6.14+, node@14.17+).

Firebase Setup

1. Navigate to Firebase website
2. Click on Add project
3. Enter project name (lidar-fb)
4. Click on continue
5. In the Project Overview page, click on </> to create new web app
6. Register Web App with a nickname (lidar-fb), and click continue
7. Copy the Firebase Configuration code (firebaseConfig)
8. Paste it by overwriting the old values in src/index.js
9. Go to Realtime Database (RTDB) page, and click on Create Database
10. Choose Singapore (asia-southeast1) as the RTDB location (or whichever closest)
11. Choose to Start in test mode
12. Click in Rules tab and edit the json document with the following code and Publish changes:

{
    "rules": {
        ".read": "true", // Can be read for forever, by anyone.
        ".write": "true" // Can be written in forever, by anyone.
    }
}

13. (Optional) To modify the Rules, read more about them here

Firebase is now setup and ready for use!

Obtaining Source Code and Building

The source code is available here.

Run the following commands:

cd ~ #directory where the project is to be located
git clone https://github.com/bhaskar-anand-iith/lidar-fb
cd lidar-fb/ #root of project
npm i #installing dependencies

Troubleshooting Build Errors

• Version Error: ensure npm@6.14+, and node@14.17+

npm -v
node -v

Execution

For testing locally:

npm run dev #runs the "dev" srcipt defined in package.json

If changes are made to src/index.js, then dist/bundle.js has to be recompiled using the command:

npm run webpack

Webpage Operation

The Sender and receiver must be in the same room. The room can be chosen from the URL (Address Bar). By default, an 8-digit random ID is assigned.

Sender/Sensor side: Once the webpage has loaded, the webpage automatically subscribes to /n2b_data rostopic, and immediately starts publishing to the RTDB.

Receiver/Visualizer side: Once the webpage has loaded, the user must click on start button to subscribe to the RTDB, and then starts publishing to /b2n_data rostopic. When the stop button is clicked, the RTDB is unsubscribed.

ROSTopic Specifications

Subscribes to /n2b_data rostopic (from native c++ code)

Publishes to /b2n_data rostopic (from browser)

Deployment

The app has been deployed on Heroku. It is connected with GitHub (through a webhook) and automatically deploys any changes that are made to the main branch (by default) in the connected GitHub repository.

Requires a Heroku account

Heroku Setup

1. Go to Heroku Dashboard
2. Click on New -> Create new app
3. Enter App name, choose a region, and click Create app
4. In the Deploy tab, set the deployment method to GitHub
5. Search for the repository name (lidar-fb) (you must be owner of repository on GitHub. Explore GitHub Teams for more features)
6. Enable Automatic Deploys and Deploy Branch (main)

The webapp will take some time to be built and deployed. The webapp can be accessed at App-name.herokuapp.com

For additional build information, access the Activity tab and click on the build of choice.

Troubleshooting Common Errors

• Not receiving any data from RTDB: check network status, firebase usage limits
• Receiving data but no visualization in RViz: check if roscore, ros-bridge server, and decoder are running.
• No data is being sent: check if roscore, ros-bridge server, and encoder are running, firebase usage limits.
• Latency is continuously increasing over time: bandwidth is insufficient, find a better network.