write

Write logs to ROS 2 bag log file

Since R2022b

Syntax

write(bagwriter,topic,timestamp,message)

Description

write(bagwriter,topic,timestamp,message) writes logs to the ROS 2 bag log file. A log contains a topic, its corresponding timestamp, and a ROS message.

Examples

Write Log Using ros2bagwriter Object by Reading Messages from ROS 2 Bag 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");

Get all the information from the ROS 2 bag log file.

bag2info = ros2("bag","info",folderPath);

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

bag = ros2bagreader(folderPath);
bag.AvailableTopics

ans=4×3 table
                NumMessages         MessageType                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   MessageDefinition                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
                ___________    _____________________    _____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

    /clock       1.607e+05     rosgraph_msgs/Clock      {'%↵% For more information, see https://design.ros2.org/articles/clock_and_time.html.↵builtin_interfaces/Time clock'                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              }
    /cmd_vel             3     geometry_msgs/Twist      {'↵Vector3  linear↵Vector3  angular'                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              }
    /odom             5275     nav_msgs/Odometry        {'% The pose in this message should be specified in the coordinate frame given by header.frame_id↵% The twist in this message should be specified in the coordinate frame given by the child_frame_id↵↵% Includes the frame id of the pose parent.↵std_msgs/Header header↵↵% Frame id the pose points to. The twist is in this coordinate frame.↵char child_frame_id↵↵% Estimated pose that is typically relative to a fixed world frame.↵geometry_msgs/PoseWithCovariance pose↵↵% Estimated linear and angular velocity relative to child_frame_id.↵geometry_msgs/TwistWithCovariance twist'                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              }
    /scan              892     sensor_msgs/LaserScan    {'%↵% If you have another ranging device with different behavior (e.g. a sonar↵% array), please find or create a different message, since applications↵% will make fairly laser-specific assumptions about this data↵↵std_msgs/Header header       % timestamp in the header is the acquisition Time of↵                             % the first ray in the scan.↵                             %↵                             % in frame frame_id, angles are measured around↵                             % the positive Z axis (counterclockwise, if Z is up)↵                             % with zero angle being forward along the x axis↵↵single angle_min             % start angle of the scan [rad]↵single angle_max             % end angle of the scan [rad]↵single angle_increment       % angular distance between measurements [rad]↵↵single time_increment        % Time between measurements [seconds] - if your scanner↵                             % is moving, this will be used in interpolating position↵                             % of 3d points↵single scan_time             % Time between scans [seconds]↵↵single range_min             % minimum range value [m]↵single range_max             % maximum range value [m]↵↵single[] ranges              % range data [m]↵                             % (Note: values < range_min or > range_max should be discarded)↵single[] intensities         % intensity data [device-specific units].  If your↵                             % device does not provide intensities, please leave↵                             % the array empty.'}

Select a subset of the messages by applying filters to the topic and timestamp.

start = bag.StartTime;
odomBagSel = select(bag,"Time",[start start+30],"Topic","/odom")

odomBagSel = 
  ros2bagreader with properties:

           FilePath: 'C:\Users\echakrab\OneDrive - MathWorks\Documents\MATLAB\ExampleManager\echakrab.Bdoc23a.ROS2transform\ros-ex95368813\ros2_netwrk_bag\ros2_netwrk_bag.db3'
          StartTime: 1.6020e+09
            EndTime: 1.6020e+09
    AvailableTopics: [1×3 table]
        MessageList: [801×3 table]
        NumMessages: 801

Get the messages in the selection.

odomMsgs = readMessages(odomBagSel);

Retrieve the list of timestamps from the topic.

timestamps = odomBagSel.MessageList.Time;

Create a ros2bagwriter object and a ROS 2 bag file in the specified folder.

bagWriter = ros2bagwriter("myRos2bag");

Write the messages related to the "/odom" topic to the ROS 2 bag file.

write(bagWriter,"/odom",timestamps,odomMsgs)

Close the bag file, remove the ros2bagwriter object from memory, and clear the associated object.

delete(bagWriter)
clear bagWriter

Load the new ROS 2 bag log file.

bagOdom = ros2bagreader("myRos2bag");

Retrieve messages from the ROS 2 bag log file.

msgs = readMessages(bagOdom);

Plot the coordinates for the messages in the ROS 2 bag log file.

To run the example again, remove the myRos2bag file and the ros2_netwrk_bag file from memory.

plot(cellfun(@(msg) msg.pose.pose.position.x,msgs),cellfun(@(msg) msg.twist.twist.angular.z,msgs))

Create Single Log and Write to ROS 2 Bag File

Create a ros2bagwriter object and a ROS 2 bag file in the specified folder.

bagWriter = ros2bagwriter("myRos2bag");

Write a single log to the ROS 2 bag file.

topic = "/odom";
message = ros2message("nav_msgs/Odometry");
timestamp = ros2time(1.6170e+09);
write(bagWriter,topic,timestamp,message)

Close the bag file, remove the ros2bagwriter object from memory, and clear the associated object.

delete(bagWriter)
clear bagWriter

Create Multiple Logs and Write to ROS 2 Bag File

Create a ros2bagwriter object and a ROS 2 bag file in the specified folder. Specify the cache size for each message.

bagWriter = ros2bagwriter("bag_files/my_bag_file",CacheSize=1500);

Write multiple logs to the ROS 2 bag file.

message1 = ros2message("nav_msgs/Odometry");
message2 = ros2message("geometry_msgs/Twist");
message3 = ros2message("sensor_msgs/Image");
write(bagWriter, ...
      ["/odom","cmd_vel","/camera/rgb/image_raw"], ...
      {ros2time(1.6160e+09),ros2time(1.6170e+09),ros2time(1.6180e+09)}, ...
      {message1,message2,message3})

Close the bag file, remove the ros2bagwriter object from memory, and clear the associated object.

delete(bagWriter)
clear bagWriter

Create Multiple Logs for Same Topic and Write to ROS 2 Bag File

Create a ros2bagwriter object and a ROS 2 bag file in the specified folder.

bagWriter = ros2bagwriter("myBag");

Write multiple logs for the same topic to the ROS 2 bag file.

pointMsg1 = ros2message("geometry_msgs/Point");
pointMsg2 = pointMsg1;
pointMsg3 = pointMsg1;
pointMsg1.x = 1;
pointMsg2.x = 2;
pointMsg3.x = 3;
write(bagWriter, ...
      "/point", ...
      {1.6190e+09,1.6200e+09,1.6210e+09}, ...
      {pointMsg1,pointMsg2,pointMsg3})

Close the bag file, remove the ros2bagwriter object from memory, and clear the associated object.

delete(bagWriter)
clear bagWriter

Input Arguments

bagwriter — ROS 2 log file writer

ros2bagwriter object

ROS 2 log file writer, specified as a ros2bagwriter object.

topic — ROS 2 topic names

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

ROS 2 topic names, 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 — Timestamps of ROS 2 messages

Time object | numeric scalar | structure | cell array of Time objects | cell array of nonnegative numeric scalars | cell array of structures

Timestamps of the ROS 2 messages, specified as Time objects, numeric scalar, structure, cell array of Time objects, cell array of nonnegative numeric scalars, or cell array of structures. Specify multiple timestamps by using a cell array. Create a Time object using ros2time.

Example: 1625559291

Example: ros2time(node, "now")

Example: {1625559291,1625559292}

message — ROS 2 messages

Message object | structure | cell array of Message objects | cell array of structures

ROS 2 messages, specified as a Message object, structure, cell array of Message objects, or cell array of structures. Specify multiple messages by using a cell array. Create a Message object using ros2message.

Example: ros2message("nav_msgs/Odometry")

Example: ros2message("nav_msgs/Odometry",DataFormat="struct")

Example: {ros2message("nav_msgs/Odometry"),ros2message("geometry_msgs/Twist")}

Version History

Introduced in R2022b