ROS_tutorial

Introduction

This repository includes some example codes for ROS beginners to understand how ROS works. You can learn more from this repository. For ROS installation, please see the guide at the end.

Type			Communication Pattern	Message Type	Typical Usage
topic	Talker-Listener	publish-subscribe	asynchronous	message(*.msg)	sensor data, control command, ...
service	Client-Server	request-response	synchronous	service(*.srv)	specific actions, switch, photo, ...

• src: roscpp
• scripts: rospy
• msg: gps.msg
• srv: Greeting.srv

How to Run

1. Run Examples

1) Clone this repo from GitHub, in case you haven't done it yet:

cd ~/Documents/catkin_ws/src
git clone https://github.com/Jarvis861/ROS_tutorial.git

2) Open ROS workspace and compile

cd ~/Documents/catkin_ws && catkin_make

3) Run the following commands in 3 terminals.

• topic (roscpp)

roscore
rosrun my_demo listener
rosrun my_demo talker

• service (roscpp)

roscore
rosrun my_demo server
rosrun my_demo client

• topic (rospy)

roscore
rosrun my_demo py_listener.py
rosrun my_demo py_talker.py

• service (rospy)

roscore
rosrun my_demo py_server.py
rosrun my_demo py_client.py

Note: rospy cannot be found probably due to lack of permission, run

cd ~/Documents/catkin_ws/src/ROS_tutorial/my_demo/
chmod u+x scripts/ -R

2. (Optional) Write an Example

1) Create a package:

cd ~/catkin_ws/src
catkin_create_pkg ${PACKAGE_NAME} roscpp rospy std_msgs

2) Define a message (or service):

cd ${PACKAGE_NAME}
mkdir msg && cd msg
gedit ${MESSAGE_NAME}.msg

3) Initialize .msg or .srv :

cd ~/catkin_ws
catkin_make

For roscpp, you will find header files in ~/catkin_ws/devel/include/${PACKAGE_NAME}/${MESSAGE_NAME}.msg.

For rospy, the path is ~/catkin_ws/devel/lib/python3/dist-packages/${PACKAGE_NAME}/msg/__init__.py.

4) Configure CMakeLists.txt and Package.xml for roscpp.

Install and Configure ROS

1) Install ROS Noetic. You can refer to this installation guide.

2) Create a workspace and initialize:

mkdir -p ~/Documents/catkin_ws/src
cd ~/Documents/catkin_ws/src
catkin_init_workspace

cd ~/Documents/catkin_ws
catkin_make

3) Configure ROS environment:

• Open your .bashrc file:

sudo gedit ~/.bashrc

and make sure the following in .bashrc. Here the ROS version is noetic and the workspace path is ~/Documents/catkin_ws.

# Set ROS noetic
source /opt/ros/noetic/setup.bash
source ~/Documents/catkin_ws/devel/setup.bash

• Recommend to add shortcut keys in your .bash_aliases file:

sudo gedit ~/.bash_aliases

and copy the following to .bash_aliases:

######### ROS workspace #########
alias cw='cd ~/Documents/catkin_ws'
alias cs='cd ~/Documents/catkin_ws/src'
alias cm='cd ~/Documents/catkin_ws && catkin_make'

• Source .bashrc or restart your terminal so the path changes take effect:

source ~/.bashrc