ros2bagreader

Access ROS 2 bag log file information

Since R2021a

Description

The ros2bagreader object is an index of the messages within a ROS 2 bag file. You can use it to extract message data from a ROS 2 bag file or select messages based on specific criteria.

Creation

Syntax

bagreader = ros2bagreader(folderpath)

Description

bagreader = ros2bagreader(folderpath) creates an indexable ros2bagreader object, bagreader, that contains all the messages from the ROS 2 bag file at the input path filepath. The folderpath input sets the value of the FilePathproperty.

ROS 2 bag files are used for storing message data. Their primary use is in the logging of messages transmitted over a ROS 2 network. The resulting bag file can be used for offline analysis, visualization, and storage. MATLAB provides functionality for reading existing bag files.

Note

If the ROS 2 bag log file contains custom messages, create custom messages for MATLAB using ros2genmsg function before creating the ros2bagreader object.

Properties

FilePath — Absolute path to ROS 2 bag file

character vector

This property is read-only.

Absolute path to the ROS 2 bag files, specified as a character vector.

Data Types: char

StartTime — Timestamp of first message

scalar

This property is read-only.

Timestamp of the first message, specified as a scalar in seconds.

Data Types: double

EndTime — Timestamp of last message

scalar

This property is read-only.

Timestamp of the last message, specified as a scalar in seconds.

Data Types: double

NumMessages — Number of messages

scalar

This property is read-only.

Number of messages, specified as a scalar.

Data Types: double

AvailableTopics — Table of available topics

table

This property is read-only.

Table of available topics, specified as a table. Each row in the table lists one topic, the number of messages for this topic, the message type, and the message definition.

Data Types: table

MessageList — List of messages

table

This property is read-only.

List of messages, specified as a table. Each row in the table lists one message.

Data Types: table

Object Functions

readMessages	Read messages from ros2bagreader object
select	Select subset of messages in ros2bagreader

Examples

Read Messages from ROS 2 Bag Log File

Extract the zip file that contains the ROS 2 bag log file and specify the full path to the log folder.

unzip('ros2_netwrk_bag.zip');
folderPath = fullfile(pwd,'ros2_netwrk_bag');

Create a ros2bagreader object that contains all messages in the log file.

bag = ros2bagreader(folderPath);

Get information on the contents of the ros2bagreader object.

baginfo = ros2("bag","info",folderPath)

baginfo = struct with fields:
         Path: '/tmp/Bdoc23a_2213998_1465327/tp20a21dc3/ros-ex96596996/ros2_netwrk_bag/ros2_netwrk_bag.db3'
      Version: '1'
    StorageId: 'sqlite3'
     Duration: 207.9020
        Start: [1x1 struct]
          End: [1x1 struct]
         Size: 16839538
     Messages: 166867
        Types: [4x1 struct]
       Topics: [4x1 struct]

Get all the messages in the ros2bagreader object.

msgs = readMessages(bag);

Select a subset of the messages, filtered by topic.

bagSel = select(bag,"Topic","/odom");

Get the messages in the selection.

msgsFiltered = readMessages(bagSel);

Version History

Introduced in R2021a

R2022b: ros2bagreader was renamed

The ros2bagreader object was renamed from ros2bag. Use ros2bagreader when creating the object.

R2022a: folderpath Input

• The ros2bagreader object in Foxy can accept file name of the ROS 2 bag log file (.db3) as the folderpath input, when there is no metadata.yaml file.

• If there is metadata.yaml file along with the .db3 file in a folder, it accepts the folder name as the folderpath input.

R2022a: ROS 2 Bag Log File Version

The ros2bagreader object in Foxy can accept different versions of bag file from version 1 to 4.

R2022a: Empty Messages

The ros2bagreader object in Foxy discards empty messages recorded on a topic. Whereas in Dashing the ros2bagreader object accepts /rosout and /param_events topics.