readMessages

R2026b

Read messages from ros2bagreader object

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    Syntax

    msgs = readMessages(bag)
    msgs = readMessages(bag,rows)

    Description

    msgs = readMessages(bag) returns data from all messages in the ros2bagreader object bag. The function returns the messages as a cell array of structures.

    example

    msgs = readMessages(bag,rows) returns data from the messages in the rows specified by rows.Valid row indices range from 1 to bag.NumMessages. readMessages begins reading as soon as the requested index range has been indexed in the background, without waiting for the entire message list to be built. If the requested range extends beyond the currently indexed portion, MATLAB® waits until that range becomes 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\user\OneDrive - MathWorks\Documents\MATLAB\ExampleManager\user.Bdoc26b\ros-ex96596996\ros2_netwrk_bag'
      FileInformation: "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]
    CompressionFormat: 'none'
      CompressionMode: 'none'

    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\user\OneDrive - MathWorks\Documents\MATLAB\ExampleManager\user.Bdoc26b\ros-ex96596996\ros2_netwrk_bag'
      AvailableBags: "ros2_netwrk_bag.db3"
          StartTime: 1.6020e+09
            EndTime: <preparing>
    AvailableTopics: [1×3 table]
    AvailableFrames: {0×1 cell}
        MessageList: <preparing>
        NumMessages: 5275

    Get the messages in the selection.

    msgsFiltered = readMessages(bagSel);

    Input Arguments

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    Messages in the ros2bagreader object, specified as a ros2bagreader object.

    Rows of the ros2bagreader object, specified as an n-element vector. n is the number of rows to retrieve messages from. Each entry in the vector corresponds to a numbered message in the bag. The range of the rows is [1 bag.NumMessages].

    Output Arguments

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    ROS 2 message data, returned as a cell array of structures.

    Version History

    Introduced in R2021a

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    See Also

    Objects

    Functions