Rosbag2

The rosbags.rosbag2 package provides a conformant implementation of rosbag2. It provides read-write access to raw message data saved inside rosbag2 containers, and supports all features present in the C++ reference implementation.

Supported Versions

All versions up to the current (ROS2 Iron) version 8 are supported.

Supported Features

Rosbag2 is a flexible format that supports plugging different serialization methods, compression formats, and storage containers together. The rosbag2 C++ reference implementation is build around plugins that provide serialization, compression, and storage. This project implements all rosbag2 core plugins that are distributed with the C++ reference implementation.

Serializers:
  • cdr (without wstring)

Compressors:
  • zstd

Storages:
  • sqlite3

  • mcap

Writing rosbag2

Instances of the Writer class can create and write to new rosbag2 files. It is usually used as a context manager. Before the first message of a topic can be written, its topic must first be added to the bag. The following example shows the typical usage pattern:

from rosbags.rosbag2 import Writer
from rosbags.typesys import Stores, get_typestore


# Create a typestore and get the string class.
typestore = get_typestore(Stores.LATEST)
String = typestore.types['std_msgs/msg/String']

# Create writer instance and open for writing.
with Writer('/home/ros/rosbag_2020_03_24') as writer:
    # Add new connection.
    topic = '/chatter'
    msgtype = String.__msgtype__
    connection = writer.add_connection(topic, msgtype, typestore=typestore)

    # Serialize and write message.
    timestamp = 42
    message = String('hello world')
    writer.write(connection, timestamp, typestore.serialize_cdr(message, msgtype))

Reading rosbag2

Instances of the Reader class are used to read rosbag2 metadata and its contents. Most of the metadata is available on Reader instances right away, messages can only be accessed after the bag has been opened. To this end it is recommended to use the Reader as a context manager. The following example shows the typical usage pattern:

from rosbags.rosbag2 import Reader
from rosbags.typesys import Stores, get_typestore


# Create a typestore and get the string class.
typestore = get_typestore(Stores.LATEST)

# Create reader instance and open for reading.
with Reader('/home/ros/rosbag_2020_03_24') as reader:
    # Topic and msgtype information is available on .connections list.
    for connection in reader.connections:
        print(connection.topic, connection.msgtype)

    # Iterate over messages.
    for connection, timestamp, rawdata in reader.messages():
        if connection.topic == '/imu_raw/Imu':
            msg = typestore.deserialize_cdr(rawdata, connection.msgtype)
            print(msg.header.frame_id)

    # The .messages() method accepts connection filters.
    connections = [x for x in reader.connections if x.topic == '/imu_raw/Imu']
    for connection, timestamp, rawdata in reader.messages(connections=connections):
        msg = typestore.deserialize_cdr(rawdata, connection.msgtype)
        print(msg.header.frame_id)