write
Description
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_2679053_267941/tpc8318d0a/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_2679053_267941/tpc8318d0a/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_2679053_252188/tpa87f0a22/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 0.60795 seconds. Initializing ROS master on http://172.20.225.136:59404. Initializing global node /matlab_global_node_40560 with NodeURI http://dcc882528glnxa64:41373/ and MasterURI http://localhost:59404.
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_2679053_252188/tpa87f0a22/ros-ex26181333/bagfile.bag' StartTime: 1.7215e+09 EndTime: 1.7215e+09 NumMessages: 1 Compression: 'lz4' ChunkSize: 1500 Bytes FileSize: 4172 Bytes
Shut down the ROS network.
rosshutdown
Shutting down global node /matlab_global_node_40560 with NodeURI http://dcc882528glnxa64:41373/ and MasterURI http://localhost:59404. Shutting down ROS master on http://172.20.225.136:59404.
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_2679053_252188/tpa87f0a22/ros-ex26181333/bagfile.bag' StartTime: 1.7215e+09 EndTime: 1.7215e+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.
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
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