write

Write logs to rosbag log file

Since R2021b

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.

Examples

Write Log to rosbag File Using rosbagwriter Object

Retrieve all the information from the rosbag log file.

rosbag('info','path_record.bag')

Path:     /tmp/Bdoc26a_3146167_784151/tp46202a31/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/Bdoc26a_3146167_784151/tp46202a31/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

Create rosbag File Using rosbagwriter Object

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/Bdoc26a_3146167_782271/tpcab6618d/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 0.87804 seconds.
Initializing ROS master on http://172.20.24.202:55211.
Initializing global node /matlab_global_node_57554 with NodeURI http://dcc2856820glnxa64:35005/ and MasterURI http://localhost:55211.

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/Bdoc26a_3146167_782271/tpcab6618d/ros-ex26181333/bagfile.bag'         
      StartTime: 1.7694e+09                                                                  
        EndTime: 1.7694e+09                                                                  
    NumMessages: 1                                                                           
    Compression: 'lz4'                                                                       
      ChunkSize: 1500                                                                   Bytes
       FileSize: 4172                                                                   Bytes

Shut down the ROS network.

rosshutdown

Shutting down global node /matlab_global_node_57554 with NodeURI http://dcc2856820glnxa64:35005/ and MasterURI http://localhost:55211.
Shutting down ROS master on http://172.20.24.202:55211.

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/Bdoc26a_3146167_782271/tpcab6618d/ros-ex26181333/bagfile.bag'
          StartTime: 1.7694e+09
            EndTime: 1.7694e+09
        NumMessages: 1
    AvailableTopics: [1×3 table]
    AvailableFrames: {0×1 cell}
        MessageList: [1×4 table]

bagreader.AvailableTopics

ans=1×3 table
             NumMessages       MessageType                                                                                                                                                                                                                                                                                                           MessageDefinition                                                                                                                                                                                                                                                                                                     
             ___________    _________________    __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

    /odom         1         nav_msgs/Odometry    {'std_msgs/Header Header↵  uint32 Seq↵  Time Stamp↵  char FrameId↵char ChildFrameId↵geometry_msgs/PoseWithCovariance Pose↵  geometry_msgs/Pose Pose↵    geometry_msgs/Point Position↵      double X↵      double Y↵      double Z↵    geometry_msgs/Quaternion Orientation↵      double X↵      double Y↵      double Z↵      double W↵  double[36] Covariance↵geometry_msgs/TwistWithCovariance Twist↵  geometry_msgs/Twist Twist↵    geometry_msgs/Vector3 Linear↵      double X↵      double Y↵      double Z↵    geometry_msgs/Vector3 Angular↵      double X↵      double Y↵      double Z↵  double[36] Covariance↵'}

Input Arguments

bagwriter — ROS log file writer

rosbagwriter object

ROS log file writer, specified as a rosbagwriter object.

topic — ROS topic name

string scalar | character vector | cell array of string scalars | cell array of character vectors

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 — Timestamp of ROS message

Time object handle | numeric scalar | structure | cell array of Time object handles | cell array of numeric scalars | cell array of structures

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}

message — ROS message

Message object handle | structure | cell array of Message object handles | cell array of structures

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