ros2bagwriter

Create and write logs to ROS 2 bag log file

Since R2022b

Description

Use the ros2bagwriter object to create a ROS 2 bag file in a folder that you specify. Use the write function to write logs to the ROS 2 bag file. Each log contains a topic, its corresponding timestamp, and a ROS 2 message. After writing the logs to the ROS 2 bag file, call the delete function to close the opened ROS 2 bag file, which also generates the metadata file with .yaml extension and removes the ros2bagwriter object from memory. You can see this metadata.yaml file in the same folder where the bag file is generated. The ros2bagwriter object supports sqlite3 (DB3) storage format.

Note

The ros2bagwriter object locks the created ROS 2 bag file. to use the ROS 2 bag file, delete and clear the ros2bagwriter object.

Creation

Syntax

bagWriter = ros2bagwriter(path)

bagWriter = ros2bagwriter(path,Name=Value)

Description

bagWriter = ros2bagwriter(path) creates a ROS 2 bag file in the location specified by path and returns its corresponding ros2bagwriter object. Use the object to write records into the ROS 2 bag file. Use the path input argument to set the Path property.

The name of the ROS 2 bag file is the name of the folder containing it. If the folders in path are not available, the object creates them and places the ROS 2 bag file accordingly.

bagWriter = ros2bagwriter(path,Name=Value) sets the SplitSize, SplitDuration, CompressionFormat, and CompressionMode properties using name-value arguments.

SplitSize property enables you to set the maximum size of the bag files to a value which will split the bag files after the size of the logged data reaches the specified value. You can also set the maximum bag file duration using SplitDuration property which will split the bag files after reaching the specified elapsed time. If you specify both SplitSize and SplitDuration properties, the bag file will split at the first threshold. You can specify these options and enable compression. You can also create a compressed ROS 2 bag file with ZSTD compression format and write messages to it.

Properties

Path — Path to ROS 2 bag folder

string scalar | character vector

Note

This property becomes a read-only after creation of the object.

Path to the ROS 2 bag folder, specified as a string scalar or character vector.

Data Types: char | string

StartTime — Earliest timestamp of messages written to ROS 2 bag file

nonnegative numeric scalar

This property is read-only.

Earliest timestamp of the messages written to the ROS 2 bag file, specified as a nonnegative numeric scalar in seconds.

Data Types: single | double

EndTime — Latest timestamp of messages written to ROS 2 bag file

nonnegative numeric scalar

This property is read-only.

Latest timestamp of the messages written to the ROS 2 bag file, specified as a nonnegative numeric scalar in seconds.

Data Types: single | double

NumMessages — Number of messages written to ROS 2 bag file

nonnegative numeric scalar

This property is read-only.

Number of messages written to the ROS 2 bag file, specified as a nonnegative numeric scalar.

Data Types: single | double

CacheSize — Size of cache for writing messages to ROS 2 bag file

104857600 (default) | nonnegative integer

This property is read-only.

Size of the cache for writing messages to the ROS 2 bag file, specified as a positive integer in bytes. This value specifies the total size of the messages, that the buffer of the cache holds in the object. If you reduce this value, the object writes more messages to the disk, which consumes more time and decreases performance of the drive.

Data Types: uint64

StorageFormat — Storage format of ROS 2 bag file

'sqlite3'

This property is read-only.

Storage format of the ROS 2 bag file, specified as 'sqlite3'.

Data Types: char | string

SerializationFormat — Serialization format of messages in ROS 2 bag file

'cdr'

This property is read-only.

Serialization format of messages in the ROS 2 bag file, specified as 'cdr'. This value is the default binary serialization format used by Data Distribution Service (DDS), which is the default middleware of ROS 2.

Data Types: char | string

SplitSize — Size of ROS 2 bag file that act as threshold before splitting

Inf (default) | nonzero positive numeric scalar

Size of the ROS 2 bag file which acts as a threshold value to enable splitting, specified as a nonzero positive numeric scalar in kilobytes (kB). The specified value must be greater than 84 kB.

For example, if SplitSize is set to 100 kB, it creates a new bag after the size of the logged data equals to 100 kB. The default value Inf writes data to a single file.

Data Types: double | uint64

SplitDuration — Time elapsed in writing messages to bag file that act as threshold before splitting

Inf (default) | nonzero positive numeric scalar | struct

Time elapsed in writing a message to a ROS 2 bag file, which acts as a threshold value to enable splitting, specified as one of these values:

• Nonzero positive numeric scalar – Time elapsed in seconds.

• Structure – ros2message entity of builtin_interfaces/Time and builtin_interfaces/Duration message types.

For example, if SplitDuration is set to 5 seconds, it creates a new bag after every 5 seconds of duration. The default value Inf writes data to a single file.

Data Types: double | uint64 | struct

CompressionFormat — Compression format for creating ROS 2 bag file

"none" (default) | "zstd"

Compression format for creating a ROS 2 bag file, specified as "none" or "zstd". To use no compression format, set this CompressionFormat property to "none". To use the ZSTD compression format, set this property to "zstd" and the CompressionMode to "file" or "message".

Data Types: char | string

CompressionMode — Compression mode for ROS 2 bag file

"none" (default) | "file" | "message"

Compression mode for a ROS 2 bag file, specified as "none", "file" or "message". To use no compression format, set this property and the CompressionFormat property to "none". To use the ZSTD compression format, set the CompressionFormat property to "zstd" and the CompressionMode property to "file" to compress each bag file or "message" to compress each message in the bag file.

Data Types: char | string

Object Functions

write	Write logs to ROS 2 bag log file
delete	Remove ros2bagwriter object from memory

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

Write Multiple Logs to ROS 2 Bag File Using Split Options

Create a ros2bagwriter object and multiple ROS 2 bag files in the specified folder. Specify the size for each bag file as 100 kB as a threshold for splitting using the SplitSize property. This will split the bag file into chunks of 100 kB each.

bagWriter1 = ros2bagwriter("new_bag_files/bag_split_size",SplitSize=100);

Create another ros2bagwriter object and specify a duration of 60 seconds using the SplitDuration property, before the bag splits. This will split the bag file into 60-second chunks each.

bagWriter2 = ros2bagwriter("new_bag_files/bag_split_duration",SplitDuration=60);

Write multiple logs to the ROS 2 bag files.

msg1 = ros2message("nav_msgs/Odometry");
msg2 = ros2message("geometry_msgs/Twist");
msg3 = ros2message("sensor_msgs/Image");
msgTime1 = ros2time(1.6160e+09);
msgTime2 = ros2time(1.6170e+09);
msgTime3 = ros2time(1.6180e+09);
for i=1:100
   msgTime1.sec = msgTime1.sec+1;
   msgTime2.sec = msgTime1.sec+1;
   msgTime3.sec = msgTime2.sec+1;
   write(bagWriter1, ...
         ["/odom","cmd_vel","/camera/rgb/image_raw"], ...
         {msgTime1,msgTime2,msgTime3}, ...
         {msg1,msg2,msg3})
   write(bagWriter2, ...
         ["/odom","/camera/rgb/image_raw"], ...
         {msgTime1,msgTime2}, ...
         {msg1,msg2})
end

Close the bag files, remove the ros2bagwriter objects from memory, and clear the associated objects.

delete(bagWriter1)
delete(bagWriter2)
clear bagWriter1
clear bagWriter2

Write Multiple Logs to ROS 2 Bag File Using Compression Options

Create a ros2bagwriter object and a ROS 2 bag file in the specified folder. Specify the compression format as zstd and compression mode as file.

bagWriter1 = ros2bagwriter("new_bag_files/bag_file_compressed", ...
                           CompressionFormat="zstd",CompressionMode="file");

Create another ros2bagwriter object and a ROS 2 bag file in the specified folder. Specify the compression format as zstd and compression mode as message.

bagWriter2 = ros2bagwriter("new_bag_files/bag_message_compressed", ...
                           CompressionFormat="zstd",CompressionMode="message");

Write multiple logs to the ROS 2 bag files.

msg1 = ros2message("nav_msgs/Odometry");
msg2 = ros2message("geometry_msgs/Twist");
msg3 = ros2message("sensor_msgs/Image");
msgTime1 = ros2time(1.6160e+09);
msgTime2 = ros2time(1.6170e+09);
msgTime3 = ros2time(1.6180e+09);
for i=1:100
   msgTime1.sec = msgTime1.sec+1;
   msgTime2.sec = msgTime1.sec+1;
   msgTime3.sec = msgTime2.sec+1;
   write(bagWriter1, ...
         ["/odom","cmd_vel","/camera/rgb/image_raw"], ...
         {msgTime1,msgTime2,msgTime3}, ...
         {msg1,msg2,msg3})
   write(bagWriter2, ...
         ["/odom","/camera/rgb/image_raw"], ...
         {msgTime1,msgTime2}, ...
         {msg1,msg2})
end

Close the bag files, remove the ros2bagwriter objects from memory, and clear the associated objects.

delete(bagWriter1)
delete(bagWriter2)
clear bagWriter1
clear bagWriter2

Version History

Introduced in R2022b

R2023b: Enable bag splitting and write compressed ROS 2 messages to ROS 2 bag file

You can now write messages to a new ROS 2 bag file by using the ros2bagwriter object with bag splitting by setting SplitSize in kilobytes and SplitDuration in seconds.

You can also create a compressed ROS 2 bag file with ZSTD compression format and write messages to it.