Contents
1 Basic Commands
All ROS 2 commands are integrated into the ros2 command. The parameter that follows indicates the type of operation: for example, node is for node operations, topic is for topic operations, and so on. Additional parameters can then specify the exact action to perform.
(1) Help command
ros2 --help(2) Run a node
ros2 run <package_name> <node_name>
# e.g.
# ros2 run turtlesim turtlesim_node
# ros2 run turtlesim turtle_teleop_key (3) View nodes
Print the node list:
ros2 node listPrint node information:
ros2 node info /<node_name>
# ros2 node info /turtlesim(4) View topics
Print the topic list:
ros2 topic listSubscribe to a topic and print its messages:
ros2 topic echo <topic_name>
# e.g.
# ros2 topic echo /turtle1/cmd_velPublish to a topic manually:
ros2 topic pub --rate <rate> <publish_topic> <data_type> <data>
# e.g.
# ros2 topic pub --rate 1 /turtle1/cmd_vel geometry_msgs/msg/Twist "{linear: {x: 2.0, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 1.8}}"(5) Services
Call a service:
ros2 service call <service_name> <service_params>
# e.g.
# ros2 service call_ /_spawn turtlesim_/srv/_Spawn_ "{x: 2, y: 2, theta: 0.2, name: 'turtle2'}"(6) Data recording
Record ROS bag data:
ros2 bag record <topic_name> -o <save_path>Play ROS bag data:
ros2 bag play <rosbag_filename>(7) Launch
Launch files in ROS 2 are described using Python. Start a launch file with:
ros2 launch <node_name> simple.launch.py(8) RViz
Start RViz to visualize information:
ros2 run rviz2 rviz22 Workspaces
(1) Create a workspace
mkdir -p ~/ros2_ws/src
cd ~/ros2_ws/src
git clone https://github.com/ros/ros_tutorials.git -b humble(2) Install dependencies automatically
cd ~/ros2_ws/
rosdep install -i --from-path src --rosdistro humble -y(3) Build the workspace
cd ~/ros2_ws/
colcon build(4) Set environment variables
source install/local_setup.sh3 Packages
(1) Create packages
cd ~/ros2_ws/src
ros2 pkg create --build-type ament_cmake c_pkg_name
ros2 pkg create --build-type ament_python python_pkg_name(2) Build packages
cd ~/ros2_ws/src
colcon build
source install/local_setup.bash4 Basic Code Examples
4.1 Create a Node
Write the node’s Python program in scripts/node_helloworld.py:
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import rclpy # ROS2 Python接口库
from rclpy.node import Node # ROS2 节点类
import time
"""
创建一个HelloWorld节点, 初始化时输出“hello world”日志
"""
class HelloWorldNode(Node):
def __init__(self, name):
super().__init__(name) # ROS2节点父类初始化
while rclpy.ok(): # ROS2系统是否正常运行
self.get_logger().info("Hello World") # ROS2日志输出
time.sleep(0.5) # 休眠控制循环时间
def main(args=None): # ROS2节点主入口main函数
rclpy.init(args=args) # ROS2 Python接口初始化
node = HelloWorldNode("node_helloworld_class") # 创建ROS2节点对象并进行初始化
rclpy.spin(node) # 循环等待ROS2退出
node.destroy_node() # 销毁节点对象
rclpy.shutdown() # 关闭ROS2 Python接口Modify the package’s setup.py file:
entry_points={
'console_scripts': [
'node_helloworld = scripts.node_helloworld:main',
],4.2 Topics
(1) Publisher
Write the publisher’s Python program in scripts/publisher_node.py:
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import rclpy # ROS2 Python接口库
from rclpy.node import Node # ROS2 节点类
from std_msgs.msg import String # 字符串消息类型
"""
创建一个发布者节点
"""
class PublisherNode(Node):
def __init__(self, name):
super().__init__(name) # ROS2节点父类初始化
self.pub = self.create_publisher(String, "chatter", 10) # 创建发布者对象（消息类型、话题名、队列长度）
self.timer = self.create_timer(0.5, self.timer_callback) # 创建一个定时器（单位为秒的周期，定时执行的回调函数）
def timer_callback(self): # 创建定时器周期执行的回调函数
msg = String() # 创建一个String类型的消息对象
msg.data = 'Hello World' # 填充消息对象中的消息数据
self.pub.publish(msg) # 发布话题消息
self.get_logger().info('Publishing: "%s"' % msg.data) # 输出日志信息，提示已经完成话题发布
def main(args=None): # ROS2节点主入口main函数
rclpy.init(args=args) # ROS2 Python接口初始化
node = PublisherNode("topic_helloworld_pub") # 创建ROS2节点对象并进行初始化
rclpy.spin(node) # 循环等待ROS2退出
node.destroy_node() # 销毁节点对象
rclpy.shutdown() # 关闭ROS2 Python接口(2) Subscriber
Write the publisher’s Python program in scripts/subscriber_node.py:
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import rclpy # ROS2 Python接口库
from rclpy.node import Node # ROS2 节点类
from std_msgs.msg import String # ROS2标准定义的String消息
"""
创建一个订阅者节点
"""
class SubscriberNode(Node):
def __init__(self, name):
super().__init__(name) # ROS2节点父类初始化
self.sub = self.create_subscription(\
String, "chatter", self.listener_callback, 10) # 创建订阅者对象（消息类型、话题名、订阅者回调函数、队列长度）
def listener_callback(self, msg): # 创建回调函数，执行收到话题消息后对数据的处理
self.get_logger().info('I heard: "%s"' % msg.data) # 输出日志信息，提示订阅收到的话题消息
def main(args=None): # ROS2节点主入口main函数
rclpy.init(args=args) # ROS2 Python接口初始化
node = SubscriberNode("topic_helloworld_sub") # 创建ROS2节点对象并进行初始化
rclpy.spin(node) # 循环等待ROS2退出
node.destroy_node() # 销毁节点对象
rclpy.shutdown() # 关闭ROS2 Python接口(3) Modify setup.py
Open the package’s setup.py file and add the following entry-point configuration:
entry_points={
'console_scripts': [
'publisher_node = scripts.publisher_node:main',
'subscriber_node = scripts.subscriber_node:main',
],
},4.3 Services
(1) Client
The client code for sending data is shown below in scripts/client.py:
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import sys
import rclpy # ROS2 Python接口库
from rclpy.node import Node # ROS2 节点类
from learning_interface.srv import AddTwoInts # 自定义的服务接口
class adderClient(Node):
def __init__(self, name):
super().__init__(name) # ROS2节点父类初始化
self.client = self.create_client(AddTwoInts, 'add_two_ints') # 创建服务客户端对象（服务接口类型，服务名）
while not self.client.wait_for_service(timeout_sec=1.0): # 循环等待服务器端成功启动
self.get_logger().info('service not available, waiting again...')
self.request = AddTwoInts.Request() # 创建服务请求的数据对象
def send_request(self): # 创建一个发送服务请求的函数
self.request.a = int(sys.argv[1])
self.request.b = int(sys.argv[2])
self.future = self.client.call_async(self.request) # 异步方式发送服务请求
def main(args=None):
rclpy.init(args=args) # ROS2 Python接口初始化
node = adderClient("service_adder_client") # 创建ROS2节点对象并进行初始化
node.send_request() # 发送服务请求
while rclpy.ok(): # ROS2系统正常运行
rclpy.spin_once(node) # 循环执行一次节点
if node.future.done(): # 数据是否处理完成
try:
response = node.future.result() # 接收服务器端的反馈数据
except Exception as e:
node.get_logger().info(
'Service call failed %r' % (e,))
else:
node.get_logger().info( # 将收到的反馈信息打印输出
'Result of add_two_ints: for %d + %d = %d' %
(node.request.a, node.request.b, response.sum))
break
node.destroy_node() # 销毁节点对象
rclpy.shutdown() # 关闭ROS2 Python接口(2) Server
The server code for requesting data is shown below in scripts/server.py:
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import rclpy # ROS2 Python接口库
from rclpy.node import Node # ROS2 节点类
from learning_interface.srv import AddTwoInts # 自定义的服务接口
class adderServer(Node):
def __init__(self, name):
super().__init__(name) # ROS2节点父类初始化
self.srv = self.create_service(AddTwoInts, 'add_two_ints', self.adder_callback) # 创建服务器对象（接口类型、服务名、服务器回调函数）
def adder_callback(self, request, response): # 创建回调函数，执行收到请求后对数据的处理
response.sum = request.a + request.b # 完成加法求和计算，将结果放到反馈的数据中
self.get_logger().info('Incoming request\na: %d b: %d' % (request.a, request.b)) # 输出日志信息，提示已经完成加法求和计算
return response # 反馈应答信息
def main(args=None): # ROS2节点主入口main函数
rclpy.init(args=args) # ROS2 Python接口初始化
node = adderServer("service_adder_server") # 创建ROS2节点对象并进行初始化
rclpy.spin(node) # 循环等待ROS2退出
node.destroy_node() # 销毁节点对象
rclpy.shutdown() # 关闭ROS2 Python接口(3) Edit setup.py
entry_points={
'console_scripts': [
'client = scripts.client:main',
'server = scripts.server:main',
],
},5 URDF-Related Content
(1) Create a package
mkdir -p ~/ros2_ws/src
cd ~/ros2_ws/src
ros2 pkg create urdf_view --build-type ament_python --dependencies rclpy --license Apache-2.0
cd urdf_view(2) Create a URDF file
mkdir urdfDownload the URDF file and save it as ~/ros2_ws/src/urdf_view/urdf/r2d2.urdf.xml.
(3) Publish the state
In the ~/ros2_ws/src/urdf_view/urdf_view/ directory, create a file named state_publisher.py and paste in the following content:
from math import sin, cos, pi
import rclpy
from rclpy.node import Node
from rclpy.qos import QoSProfile
from geometry_msgs.msg import Quaternion
from sensor_msgs.msg import JointState
from tf2_ros import TransformBroadcaster, TransformStamped
class StatePublisher(Node):
def __init__(self):
rclpy.init()
super().__init__('state_publisher')
qos_profile = QoSProfile(depth=10)
self.joint_pub = self.create_publisher(JointState, 'joint_states', qos_profile)
self.broadcaster = TransformBroadcaster(self, qos=qos_profile)
self.nodeName = self.get_name()
self.get_logger().info("{0} started".format(self.nodeName))
degree = pi / 180.0
loop_rate = self.create_rate(30)
# robot state
tilt = 0.
tinc = degree
swivel = 0.
angle = 0.
height = 0.
hinc = 0.005
# message declarations
odom_trans = TransformStamped()
odom_trans.header.frame_id = 'odom'
odom_trans.child_frame_id = 'axis'
joint_state = JointState()
try:
while rclpy.ok():
rclpy.spin_once(self)
# update joint_state
now = self.get_clock().now()
joint_state.header.stamp = now.to_msg()
joint_state.name = ['swivel', 'tilt', 'periscope']
joint_state.position = [swivel, tilt, height]
# update transform
# (moving in a circle with radius=2)
odom_trans.header.stamp = now.to_msg()
odom_trans.transform.translation.x = cos(angle)*2
odom_trans.transform.translation.y = sin(angle)*2
odom_trans.transform.translation.z = 0.7
odom_trans.transform.rotation = \
euler_to_quaternion(0, 0, angle + pi/2) # roll,pitch,yaw
# send the joint state and transform
self.joint_pub.publish(joint_state)
self.broadcaster.sendTransform(odom_trans)
# Create new robot state
tilt += tinc
if tilt < -0.5 or tilt > 0.0:
tinc *= -1
height += hinc
if height > 0.2 or height < 0.0:
hinc *= -1
swivel += degree
angle += degree/4
# This will adjust as needed per iteration
loop_rate.sleep()
except KeyboardInterrupt:
pass
def euler_to_quaternion(roll, pitch, yaw):
qx = sin(roll/2) * cos(pitch/2) * cos(yaw/2) - cos(roll/2) * sin(pitch/2) * sin(yaw/2)
qy = cos(roll/2) * sin(pitch/2) * cos(yaw/2) + sin(roll/2) * cos(pitch/2) * sin(yaw/2)
qz = cos(roll/2) * cos(pitch/2) * sin(yaw/2) - sin(roll/2) * sin(pitch/2) * cos(yaw/2)
qw = cos(roll/2) * cos(pitch/2) * cos(yaw/2) + sin(roll/2) * sin(pitch/2) * sin(yaw/2)
return Quaternion(x=qx, y=qy, z=qz, w=qw)
def main():
node = StatePublisher()
if __name__ == '__main__':
main()(4) Create a launch file
Create a ~/ros2_ws/src/urdf_view/launch folder and create a demo.launch.py file inside it.
import os
from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration
from launch_ros.actions import Node
def generate_launch_description():
use_sim_time = LaunchConfiguration('use_sim_time', default='false')
urdf_file_name = 'r2d2.urdf.xml'
urdf = os.path.join(
get_package_share_directory('urdf_view'),
urdf_file_name)
with open(urdf, 'r') as infp:
robot_desc = infp.read()
return LaunchDescription([
DeclareLaunchArgument(
'use_sim_time',
default_value='false',
description='Use simulation (Gazebo) clock if true'),
Node(
package='robot_state_publisher',
executable='robot_state+_publisher',
name='robot_state_publisher',
output='screen',
parameters=[{'use_sim_time': use_sim_time, 'robot_description': robot_desc}],
arguments=[urdf]),
Node(
package='urdf_view',
executable='state_publisher',
name='state_publisher',
output='screen'),
])(5) Update setup.py
To install the Python package correctly, we must tell the colcon build tool how to install the Python package we just created. Edit ~/ros2_ws/src/urdf_view/setup.py as follows:
Import the required libraries:
import os
from glob import glob
from setuptools import setup
from setuptools import find_packagesAdd two lines to data_files:
data_files=[
...
(os.path.join('share', package_name, 'launch'), glob(os.path.join('launch', '*launch.[pxy][yma]*'))),
(os.path.join('share', package_name), glob('urdf/*')),
],Modify the entry_points list to ensure that state_publisher can be run from the command line:
'console_scripts': [
'state_publisher = urdf_view.state_publisher:main'
],(6) Install the package
cd ~/ros2_ws
colcon build --symlink-install --packages-select urdf_view
source install/setup.bash(7) Visualize the result
Start the package:
ros2 launch urdf_view demo.launch.pyOpen a new terminal and run RViz:
rviz2
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