delete

Remove rosbag writer object from memory

Since R2021b

Syntax

delete(bagWriter)

Description

delete(bagWriter) removes the rosbagwriter object from memory. The function closes the opened rosbag file before deleting the object.

If multiple references to the rosbagwriter object exist in the workspace, deleting the rosbagwriter object invalidates the remaining reference. Use the clear command to delete the remaining references to the object from the workspace.

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.

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/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

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/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

bagWriter — ROS log file writer

rosbagwriter object

ROS log file writer, specified as a rosbagwriter object.

Version History

Introduced in R2021b