rosbagwriter
Description
Use the rosbagwriter object to create a rosbag log file and
write logs to the bag file. Each log contains a topic, its corresponding timestamp, and a ROS
message.
Note
The rosbagwriter object locks the created bag file for use, it is
necessary to delete and clear the rosbagwriter object in order to use the
bag file with a reader or perform other operations.
Creation
Description
bagwriter = rosbagwriter(filepath)path and
returns the corresponding rosbagwriter object.
If you do not specify the name of the bag file in the filepath,
the object assigns the current timestamp as the file name. If the folders you specify in
filepath are not present in the directory, the object creates them
and places the bag file accordingly. The filepath input argument sets
the FilePath
property.
bagwriter = rosbagwriter(___,Name,Value)
Properties
Examples
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 circleWriterRetrieve 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 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 bagwriterCreate 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↵'}
Version History
Introduced in R2021b
