select

Select subset of messages in rosbag

Syntax

bagreadersel = select(bagreader)

bagreadersel = select(bagreader,Name=Value)

Description

bagreadersel = select(bagreader) returns a rosbagreader object bagreadersel, that contains all of the messages in the rosbagreader object bagreader.

This function creates a copy of the rosbagreader object or returns a new rosbagreader object that contains the specified message selection.

bagreadersel = select(bagreader,Name=Value) specifies additional parameters using one or more name-value arguments. For example Topic="/odom" selects a subset of the messages, filtered by the topic /odom.

Examples

Create rosbag Selection Using rosbagreader Object

Load a rosbag log file and parse out specific messages based on the selected criteria.

Create a rosbagreader object of all the messages in the rosbag log file.

bagMsgs = rosbagreader("ros_multi_topics.bag")

bagMsgs = 
  rosbagreader with properties:

           FilePath: '/mathworks/devel/bat/Bdoc22b/build/matlab/toolbox/robotics/robotexamples/ros/data/bags/ros_multi_topics.bag'
          StartTime: 201.3400
            EndTime: 321.3400
        NumMessages: 36963
    AvailableTopics: [4x3 table]
    AvailableFrames: {0x1 cell}
        MessageList: [36963x4 table]

Select a subset of the messages based on their timestamp and topic.

bagMsgs2 = select(bagMsgs,...
    Time=[bagMsgs.StartTime bagMsgs.StartTime + 1],...
    Topic='/odom')

bagMsgs2 = 
  rosbagreader with properties:

           FilePath: '/mathworks/devel/bat/Bdoc22b/build/matlab/toolbox/robotics/robotexamples/ros/data/bags/ros_multi_topics.bag'
          StartTime: 201.3400
            EndTime: 202.3200
        NumMessages: 99
    AvailableTopics: [1x3 table]
    AvailableFrames: {0x1 cell}
        MessageList: [99x4 table]

Retrieve the messages in the selection as a cell array.

msgs = readMessages(bagMsgs2)

msgs=99×1 cell array
    {1x1 Odometry}
    {1x1 Odometry}
    {1x1 Odometry}
    {1x1 Odometry}
    {1x1 Odometry}
    {1x1 Odometry}
    {1x1 Odometry}
    {1x1 Odometry}
    {1x1 Odometry}
    {1x1 Odometry}
    {1x1 Odometry}
    {1x1 Odometry}
    {1x1 Odometry}
    {1x1 Odometry}
    {1x1 Odometry}
    {1x1 Odometry}
      ⋮

Return certain message properties as a time series.

ts = timeseries(bagMsgs2,...
    'Pose.Pose.Position.X', ...
    'Twist.Twist.Angular.Y')

  timeseries

  Timeseries contains duplicate times.

  Common Properties:
            Name: '/odom Properties'
            Time: [99x1 double]
        TimeInfo: tsdata.timemetadata
            Data: [99x2 double]
        DataInfo: tsdata.datametadata

Input Arguments

bagreader — Index of messages in rosbag

rosbagreader object

Index of the messages in the rosbag, specified as a rosbagreader object.

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: Topic="/odom" selects a subset of the messages, filtered by the topic /odom.

MessageType — ROS message type

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

ROS message type, specified as a string scalar, character vector, cell array of string scalars, or cell array of character vectors. Specify multiple message types by using a cell array.

Example: select(bagreader,MessageType={"nav_msgs/Odometry","rosgraph_msgs/Clock"})

Data Types: char | string | cell

Time — Start and end times of rosbag selection

n-by-2 vector

Start and end times of the rosbag selection, specified as an n-by-2 vector.

Example: select(bagreader,Time=[bag.StartTime,bag.StartTime+1])

Data Types: double

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: select(bagreader,Topic={"/odom","/clock"})

Data Types: char | string | cell

Output Arguments

bagreadersel — Copy or subset of rosbag messages

rosbagreader object

Copy or subset of rosbag messages, returned as a rosbagreader object.

Version History

Introduced in R2021b