select

Select subset of messages in ros2bagreader

Since R2021a

Syntax

bagsel = select(bag)

bagsel = select(bag,Name,Value)

Description

bagsel = select(bag) returns a ros2bagreader object, bagsel, that contains all of the messages in the ros2bagreader object, bag.

This function creates a copy of the ros2bagreader object or returns a new ros2bagreader object that contains the specified message selection.

bagsel = select(bag,Name,Value) provides additional options specified by one or more name-value pair arguments. For example, "Topic","/scan" selects a subset of the messages, filtered by the topic /scan.

Examples

Read Messages from ROS 2 Bag Log 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");

Create a ros2bagreader object that contains all the messages in the log file.

bagReader = ros2bagreader(folderPath);

Get information about the contents of the ros2bagreader object.

baginfo = ros2("bag","info",folderPath)

baginfo = struct with fields:
         Path: 'C:\Users\ros2_netwrk_bag\ros2_netwrk_bag.db3'
      Version: '1'
    StorageId: 'sqlite3'
     Duration: 207.9020
        Start: [1×1 struct]
          End: [1×1 struct]
         Size: 16839538
     Messages: 166867
        Types: [4×1 struct]
       Topics: [4×1 struct]

Get all the messages in the ros2bagreader object.

msgs = readMessages(bagReader);

Select a subset of the messages, filtered by topic.

bagSel = select(bagReader,"Topic","/odom")

bagSel = 
  ros2bagreader with properties:

           FilePath: 'C:\Users\ros2_netwrk_bag'
      AvailableBags: "ros2_netwrk_bag.db3"
          StartTime: 1.6020e+09
            EndTime: 1.6020e+09
    AvailableTopics: [1×3 table]
    AvailableFrames: {0×1 cell}
        MessageList: [5275×3 table]
        NumMessages: 5275

Get the messages in the selection.

msgsFiltered = readMessages(bagSel);

Input Arguments

bag — Messages in ros2bagreader object

ros2bagreader object

Messages in the ros2bagreader object, specified as a ros2bagreader 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.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: select(bag,"Topic","/scan") selects a subset of the messages, filtered by the topic /scan.

MessageType — ROS 2 message type

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

ROS 2 message type, specified as a string scalar, character vector, cell array of string scalars, or cell array of character vectors. Multiple message types can be specified with a cell array.

Example: select(bag,"MessageType",{"sensor_msgs/CameraInfo","sensor_msgs/LaserScan"})

Data Types: char | string | cell

Time — Start and end times of ROS 2 bag selection

n-by-2 vector

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

Example: select(bag,"Time",[bag.MessageList(1,1).Time,bag.MessageList(2,1).Time])

Data Types: double

Topic — ROS 2 topic name

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

ROS 2 topic name, specified as a string scalar, character vector, cell array of string scalars, or cell array of character vectors. Multiple topic names can be specified with a cell array.

Example: select(bag,"Topic",{"/scan","/clock"})

Data Types: char | string | cell

Output Arguments

bagsel — Copy or subset of ROS 2 bag messages

ros2bagreader object

Copy or subset of ROS 2 bag messages, returned as a ros2bagreader object.

Version History

Introduced in R2021a