ros2bagreader

Access ROS 2 bag log file information

Since R2021a

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    Description

    The ros2bagreader object is an index of the messages within a ROS 2 bag file. You can use this object to extract message data from a ROS 2 bag file or select messages based on specific criteria. The ros2bagreader object supports sqlite3 (DB3) and MCAP storage format.

    Creation

    Syntax

    bagReader = ros2bagreader(folderpath)

    Description

    bagReader = ros2bagreader(folderpath) creates a ros2bagreader object, bagReader, that contains all the messages from the ROS 2 bag file in the input file or folder. The folderpath input sets the FilePath property.

    You can use the ROS 2 bag files for storing messages that are transmitted over a ROS 2 network. You can then use the resulting bag file for offline analysis and visualization.

    You can read a single DB3 or MCAP file in the bag folder by specifying the folderpath as a single file. You can also read all the DB3 or MCAP files in the bag folder by specifying the folderpath as a folder. Ensure that you have read and write access to the bag folder that contains the DB3 files. However, for reading a MCAP file, you must have read access to the bag folder only.

    You can read compressed ROS 2 bag files in file or message compression mode and ZSTD compression format.

    Note

    To read compressed ROS 2 bag files, specify the folderpath as the folder location.

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

    example

    Properties

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    This property is read-only.

    Absolute path to ROS 2 bag file or folder, specified as a character vector.

    Data Types: char

    This property is read-only.

    List of available ROS 2 bag files, specified as a string array.

    Data Types: string

    This property is read-only.

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

    Data Types: double

    This property is read-only.

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

    Data Types: double

    This property is read-only.

    Number of messages, specified as a scalar.

    Data Types: double

    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

    This property is read-only.

    List of available coordinate frames, specified as a cell array of character vectors. To check whether specific transformations between frames are available, use the canTransform object function. To query a transformation, use the getTransform object function.

    Data Types: cell

    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

    readMessagesRead messages from ros2bagreader object
    selectSelect subset of messages in ros2bagreader
    timetableCreate timetable for selected message properties in ROS 2 bag file
    getTransformReturn transformation between two coordinate frames
    canTransformVerify if transformation is available

    Examples

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    Open Live Script

    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 the messages in the log file. 

    bagReader = ros2bagreader(folderPath);

    Get information about the contents of the ros2bagreader object.

    baginfo = ros2("bag","info",folderPath)
    baginfo = struct with fields:
         Path: 'C:\Users\ros2_netwrk_bag\ros2_netwrk_bag.db3'
      Version: '1'
    StorageId: 'sqlite3'
     Duration: 207.9020
        Start: [1×1 struct]
          End: [1×1 struct]
         Size: 16839538
     Messages: 166867
        Types: [4×1 struct]
       Topics: [4×1 struct]

    Get all the messages in the ros2bagreader object.

    msgs = readMessages(bagReader);

    Select a subset of the messages, filtered by topic.

    bagSel = select(bagReader,"Topic","/odom")
    bagSel = 
  ros2bagreader with properties:

           FilePath: 'C:\Users\ros2_netwrk_bag'
      AvailableBags: "ros2_netwrk_bag.db3"
          StartTime: 1.6020e+09
            EndTime: 1.6020e+09
    AvailableTopics: [1×3 table]
    AvailableFrames: {0×1 cell}
        MessageList: [5275×3 table]
        NumMessages: 5275

    Get the messages in the selection.

    msgsFiltered = readMessages(bagSel);

    Version History

    Introduced in R2021a

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    See Also

    Functions

    Topics