ENPM808X Beginner Tutorials Publisher/Subscriber

Diane Ngo

ENPM808X Fall 2021

Overview

This is a ROS Package for the beginner tutorials with creating a basic publisher and subscriber in C++. Reference: link

Dependencies

Must have the following installed:

• Ubuntu 18.04
• ROS Melodic
• C++, roscpp
• Standard library
• rqt_console
• xterm (runs the subscriber in another terminal)

Installing rqt console

sudo apt-get install ros-melodic-rqt ros-melodic-rqt-common-plugins

Installing xterm

sudo apt install xterm

Building Instructions

If there is no catkin workspace

Create catkin workspace. Go to terminal and follow these commands:

mkdir -p ~/catkin_ws/src
cd ~/catkin_ws/
catkin_make

Then source the setup.bash file with this command:

source devel/setup.bash

Now please clone the beginner_tutorials package by doing the following:

cd src/
git clone https://github.com/dngo13/beginner_tutorials.git
cd ..
catkin_make
source devel/setup.bash

Cloning into an existing catkin workspace

Go to the src directory for the catkin workspace. And then follow these steps

cd ~/catkin_ws/src/
git clone https://github.com/dngo13/beginner_tutorials.git
cd ..
catkin_make
source devel/setup.bash

Running the Program

Now that the package is built, we can run the program. In this terminal, run roscore.

Running it individually with the nodes

Open a new terminal, source it with:

source devel/setup.bash

And then run:

rosrun beginner_tutorials talker

Now, open a new terminal again, source it with:

source devel/setup.bash

And then run:

rosrun beginner_tutorials listener

You should see output in both terminals similar to ENPM808X ROS count: # and I heard: [ENPM808X ROS count: #]

Running the launch file

Open a new terminal, source it with:

source devel/setup.bash

And then run:

roslaunch beginner_tutorials pub_sub_launch.launch

Alternatively, to change the frequency:

roslaunch beginner_tutorials pub_sub_launch.launch frequency:=##

Where ## is a number of your choice. Note that a 0 or a negative number will throw a fatal error and terminate the program. A frequency greater than 25 will give a warning.

Changing the string output

To call the service first check if it is seen below:

rosservice list

You should see something like:

/ChangeStringOutput
/listener_node/get_loggers
/listener_node/set_logger_level
/rosout/get_loggers
/rosout/set_logger_level
/rqt_gui_py_node_11776/get_loggers
/rqt_gui_py_node_11776/set_logger_level
/rqt_gui_py_node_11824/get_loggers
/rqt_gui_py_node_11824/set_logger_level
/talker_node/get_loggers
/talker_node/set_logger_level

Then, run the command below to change the text, with anything between the quotes as your desired output.

rosservice call /ChangeStringOutput "New Message" 

Viewing TF Frames

To view tf frames, ensure the talker is running by making sure the launch file is running: 1st terminal: roscore 2nd terminal:

roslaunch beginner_tutorials pub_sub_launch.launch

3rd terminal:

rosrun rqt_tf_tree rqt_tf_tree

Also the pdf file for the frames (frames.pdf) is pregenerated and inside the /results directory.

Running rostest

To run the test, ensure you are in the catkin workspace first and run the below.

cd ~/catkin_ws/ 
catkin_make run_tests

Ctrl-c to end the script. You should see an output similar to:

[Testcase: testbeginner_tutorials_test] ... ok

[ROSTEST]-----------------------------------------------------------------------

[beginner_tutorials.rosunit-beginner_tutorials_test/testTalkerExists][passed]

SUMMARY
 * RESULT: SUCCESS
 * TESTS: 1
 * ERRORS: 0
 * FAILURES: 0

rostest log file is in /home/diane/.ros/log/rostest-diane-laptop-linux-19937.log

View rosbag file

There is a rosbag file already recorded in the /results directory. To view it, do the following commands in a terminal.

cd ~/catkin_ws/
source devel/setup.bash
cd src/beginner_tutorials/results
rosbag info rosbag_record.bag 

The output should be similar to this:

path:        rosbag_record.bag
version:     2.0
duration:    15.0s
start:       Nov 14 2021 17:47:16.61 (1636930036.61)
end:         Nov 14 2021 17:47:31.57 (1636930051.57)
size:        184.1 KB
messages:    876
compression: none [1/1 chunks]
types:       rosgraph_msgs/Log  [acffd30cd6b6de30f120938c17c593fb]
             std_msgs/String    [992ce8a1687cec8c8bd883ec73ca41d1]
             tf2_msgs/TFMessage [94810edda583a504dfda3829e70d7eec]
topics:      /chatter      147 msgs    : std_msgs/String   
             /rosout       293 msgs    : rosgraph_msgs/Log  (3 connections)
             /rosout_agg   289 msgs    : rosgraph_msgs/Log 
             /tf           147 msgs    : tf2_msgs/TFMessage

Recording a New Bag File

If you want to record a new bag file then launch the launch file with the following argument like below:

roslaunch beginner_tutorials pub_sub_launch.launch record_bag:=True

To disable bag recording, just ignore the record_bag param as the default value is set to false in the launch file.

Verify Listener and Rosbag play

Open a terminal and start roscore. Then in a new terminal:

cd ~/catkin_ws/
source devel/setup.bash
rosbag play src/beginner_tutorials/results/rosbag_record.bag

In a third terminal:

rosrun beginner_tutorials listener