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write

Write logs to rosbag log file

Since R2021b

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    Syntax

    write(bagwriter,topic,timestamp,message)

    Description

    write(bagwriter,topic,timestamp,message) writes a single or multiple logs to a rosbag log file. A log contains a topic, its corresponding timestamp, and a ROS message.

    example

    Examples

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    Open Live Script

    Retrieve all the information from the rosbag log file.

    rosbag('info','path_record.bag')
    Path:     /tmp/Bdoc24b_2725827_1915370/tp324d55df/ros-ex73035957/path_record.bag
Version:  2.0
Duration: 10.5s
Start:    Jul 05 2021 08:09:52.86 (1625486992.86)
End:      Jul 05 2021 08:10:03.40 (1625487003.40)
Size:     13.3 KB
Messages: 102
Types:    geometry_msgs/Point [4a842b65f413084dc2b10fb484ea7f17]
Topics:   /circle  51 msgs  : geometry_msgs/Point
          /line    51 msgs  : geometry_msgs/Point

    Create a rosbagreader object of all the messages in the rosbag log file.

    reader = rosbagreader('path_record.bag');

    Select all the messages related to the topic '/circle'.

    bagSelCircle = select(reader,'Topic','/circle');

    Retrieve the list of timestamps from the topic.

    timeStamps = bagSelCircle.MessageList.Time;

    Retrieve the messages in the selection as a cell array.

    messages = readMessages(bagSelCircle);

    Create a rosbagwriter object to write the messages to a new rosbag file.

    circleWriter = rosbagwriter('circular_path_record.bag');

    Write all the messages related to the topic '/circle' to the new rosbag file.

    write(circleWriter,'/circle',timeStamps,messages);

    Remove the rosbagwriter object from memory and clear the associated object.

    delete(circleWriter)
clear circleWriter

    Retrieve all the information from the new rosbag log file.

    rosbag('info','circular_path_record.bag')
    Path:     /tmp/Bdoc24b_2725827_1915370/tp324d55df/ros-ex73035957/circular_path_record.bag
Version:  2.0
Duration: 10.4s
Start:    Jul 05 2021 08:09:52.86 (1625486992.86)
End:      Jul 05 2021 08:10:03.29 (1625487003.29)
Size:     8.8 KB
Messages: 51
Types:    geometry_msgs/Point [4a842b65f413084dc2b10fb484ea7f17]
Topics:   /circle  51 msgs  : geometry_msgs/Point

    Load the new rosbag log file.

    readerCircle = rosbagreader('circular_path_record.bag');

    Create a time series for the coordinates.

    tsCircle = timeseries(readerCircle,'X','Y');

    Plot the coordinates.

    plot(tsCircle.Data(:,1),tsCircle.Data(:,2))
axis equal

    Figure contains an axes object. The axes object contains an object of type line.

    Open Live Script

    Create a rosbagwriter object and a rosbag file in the current working directory. Specify the compression format of the message chunks and the size of each message chunk.

    bagwriter = rosbagwriter("bagfile.bag", ...
    "Compression","lz4",...
    "ChunkSize",1500)
    bagwriter = 
  rosbagwriter with properties:

       FilePath: '/tmp/Bdoc24b_2725827_1908818/tpff73b302/ros-ex26181333/bagfile.bag'         
      StartTime: 0                                                                            
        EndTime: 0                                                                            
    NumMessages: 0                                                                            
    Compression: 'lz4'                                                                        
      ChunkSize: 1500                                                                    Bytes
       FileSize: 4117                                                                    Bytes

    Start node and connect to ROS master.

    rosinit
    Launching ROS Core...
Done in 0.75187 seconds.
Initializing ROS master on http://172.20.148.53:60580.
Initializing global node /matlab_global_node_65531 with NodeURI http://dcc867993glnxa64:42101/ and MasterURI http://localhost:60580.

    Write a single log to the rosbag file.

    timeStamp = rostime("now");
rosMessage = rosmessage("nav_msgs/Odometry");
write(bagwriter,"/odom",timeStamp,rosMessage);
bagwriter
    bagwriter = 
  rosbagwriter with properties:

       FilePath: '/tmp/Bdoc24b_2725827_1908818/tpff73b302/ros-ex26181333/bagfile.bag'         
      StartTime: 1.7256e+09                                                                   
        EndTime: 1.7256e+09                                                                   
    NumMessages: 1                                                                            
    Compression: 'lz4'                                                                        
      ChunkSize: 1500                                                                    Bytes
       FileSize: 4172                                                                    Bytes

    Shut down the ROS network.

    rosshutdown
    Shutting down global node /matlab_global_node_65531 with NodeURI http://dcc867993glnxa64:42101/ and MasterURI http://localhost:60580.
Shutting down ROS master on http://172.20.148.53:60580.

    Remove rosbag writer object from memory and clear the associated object.

    delete(bagwriter)
clear bagwriter

    Create a rosbagreader object and load all the messages in the rosbag log file. Verify the recently written log.

    bagreader = rosbagreader('bagfile.bag')
    bagreader = 
  rosbagreader with properties:

           FilePath: '/tmp/Bdoc24b_2725827_1908818/tpff73b302/ros-ex26181333/bagfile.bag'
          StartTime: 1.7256e+09
            EndTime: 1.7256e+09
        NumMessages: 1
    AvailableTopics: [1x3 table]
    AvailableFrames: {0x1 cell}
        MessageList: [1x4 table]


    bagreader.AvailableTopics
    ans=1×3 table
             NumMessages       MessageType             MessageDefinition      
             ___________    _________________    _____________________________

    /odom         1         nav_msgs/Odometry    {'std_msgs/Header Header...'}

    Input Arguments

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    ROS log file writer, specified as a rosbagwriter object.

    ROS topic name, specified as a string scalar, character vector, cell array of string scalars, or cell array of character vectors. Specify multiple topic names by using a cell array.

    Example: "/odom"

    Example: {"/odom","cmd_vel"}

    Timestamp of the ROS message, specified as a Time object handle, numeric scalar, structure, cell array of Time object handles, cell array of numeric scalars, or cell array of structures. Specify multiple timestamps by using a cell array. Create a Time object using rostime.

    Example: 1625559291

    Example: rostime("now")

    Example: rostime("now","DataFormat","struct")

    Example: {1625559291,1625559292}

    Example: {rostime("now"),rostime("now")+1}

    ROS message, specified as a Message object handle, structure, cell array of Message object handles, or cell array of structures. Specify multiple messages by using a cell array. Create a Message object using rosmessage.

    Example: rosmessage("nav_msgs/Odometry")

    Example: rosmessage("nav_msgs/Odometry","DataFormat","struct")

    Example: {rosmessage("nav_msgs/Odometry"),rosmessage("geometry_msgs/Twist")}

    Version History

    Introduced in R2021b

    See Also

    Objects

    Functions