MCAP to JSON Converter Suite

A comprehensive toolkit for converting, processing, and streaming ROS2 MCAP bag files to JSON format for analysis, visualization, and real-time data streaming.

Overview

This project provides tools to:

• Convert MCAP files to JSON: Extract ROS2 messages from MCAP bag files into line-delimited JSON format
• Stream data via WebSocket: Send JSON-formatted ROS2 data to visualization tools like PlotJuggler
• Process compressed data: Handle .bz2 compressed files seamlessly
• Decode ROS2 messages: Parse CDR-encoded messages and IDL schemas

Project Structure

mcap2json/
├── mcap2json/           # Core MCAP to JSON converter
│   ├── workspace/       # Working directory with conversion scripts
│   ├── Containerfile    # Container definition for deployment
│   ├── Makefile        # Build automation
│   └── README.md       # Converter documentation
├── plotjuggler/        # WebSocket streaming for PlotJuggler
│   ├── play_plotjuggler.py  # WebSocket streaming script
│   ├── requirements.txt     # Python dependencies
│   ├── media/          # Screenshots and documentation images
│   └── README.md       # PlotJuggler integration guide
└── README.md           # This file

Components

1. MCAP to JSON Converter (mcap2json/)

The core converter that processes ROS2 MCAP bag files and outputs JSON. Features include:

• Topic filtering and listing
• IDL schema extraction
• CDR message decoding
• Batch processing of directories
• Compressed output support

📖 Read the MCAP Converter Documentation

Quick Example:

cd mcap2json/workspace
python mcap2json.py -m rosbag.mcap -o output.json.bz2

2. PlotJuggler WebSocket Streamer (plotjuggler/)

A real-time streaming tool that sends JSON data via WebSocket for visualization in PlotJuggler:

• Asynchronous WebSocket communication
• ROS2 timestamp conversion
• Topic-based data organization
• Support for secure WebSocket (WSS)

📖 Read the PlotJuggler Integration Guide

Quick Example:

cd plotjuggler
./play_plotjuggler.py -v data.json -w ws://localhost:9871

License

Licensed under the Apache License, Version 2.0. See the source file for full license text.