您现在的位置：程式師世界 >> 編程語言 > >> 更多編程語言 >> Python

[ROS] (09) ROS Communication - msg (C++) (Python) of Topic Communication Programming

編輯：Python

文章只是個人學習過程中學習筆記,主要參考ROS教程¹²³.

[ROS]（01）創建ROS工作空間

[ROS]（02）創建&編譯ROS軟件包Package

1、概述
2、msg結構和類型
- 2.1 類型
- 2.2 舉例
3、msg命令rosmsg
4、msg的用法
- 4.1 創建msg
- 4.2 配置CMakeLists.txt
- 4.3 配置package.xml
- 4.4 編譯package
5、msg命令實操
- 5.1 rosmsg list
- 5.2 rosmsg packages
- 5.3 rosmsg package
- 5.4 rosmsg show / rosmsg info
- 5.5 rosmsg md5
6、Practical programming -- Topic communication sends custom messages
- 6.1 編寫程序（C++）
- - 6.1.1 發布者程序（talker.cpp）
  - 6.1.2 訂閱者程序（listener.cpp）
  - 6.1.3 配置CMakeLists.txt
  - 6.1.4 編譯、運行
- 6.2 編寫程序（python）
- - 6.2.1 發布者程序（talker.py）
  - 6.2.2 訂閱者程序（listener.py）
  - 6.2.3 配置CMakeLists.txt
  - 6.1.4 編譯、運行

1、概述

msg（消息）文件就是文本文件,用於描述ROS消息的字段.它們用於為不同編程語言編寫的消息生成源代碼.
msg文件存放在軟件包的msg目錄下.

2、msg結構和類型

msg⁴文件就是簡單的文本文件,每行都有一個字段類型和字段名稱.它的結構為：
fieldtype + fieldname

2.1 類型

可以使用的類型為：

int8, int16, int32, int64 (以及 uint*)
float32, float64
string
time, duration
其他msg文件
variable-length array[] 和 fixed-length array[C]

2.2 舉例

# 特殊的Header類型,它含有時間戳和ROS中廣泛使用的坐標幀信息
# 在msg文件的第一行經常可以看到Header header.
std_msgs/Header header
uint8 is_true
uint32 height
uint32 width
string child_frame_id
time stamp
geometry_msgs/PoseWithCovariance pose
geometry_msgs/TwistWithCovariance twist
uint8[] data

3、msg命令rosmsg

rosmsg顯示有關ROSMessage type information.

命令功能rosmsg showDisplays the description of the message（詳細信息）rosmsg inforosmsg show的別名,功能一樣rosmsg list列出所有消息rosmsg md5顯示md5加密的消息rosmsg packageList a package（package）的消息rosmsg packagesList packages that contain messages（packages）

4、msg的用法

4.1 創建msg

Still in the original package created beginner_tutorials Define a new message in .

# Change to the directory path of the package
roscd beginner_tutorials
# 創建msg文件夾目錄
mkdir msg
# 創建名為Num.msg的文件,and add a message field
echo "int64 num" > msg/Num.msg

4.2 配置CMakeLists.txt

1. 為已經存在裡面的find_package調用添加message_generation依賴項（）,這樣就能生成消息了.（添加 message_generation 依賴項,必須有 std_msgs .）

find_package(catkin REQUIRED COMPONENTS
roscpp
rospy
std_msgs
message_generation
)

2. Add custom message files.將你msgcustom folder*.msgFile added here.

add_message_files(
FILES
Num.msg
)

3. used to generate all definitionsmessage文件,This file needs to be added to depend onpackages.其實就是告訴編譯器,編譯 *.msg 文件時,Dependent library or package.

generate_messages(
DEPENDENCIES
std_msgs
)

4. Runtime dependencies for exported messages.

catkin_package(
...
CATKIN_DEPENDS message_runtime ...
...)

4.3 配置package.xml

Add compilation and execution dependencies.

 <build_depend>message_generation</build_depend>
<exec_depend>message_runtime</exec_depend>

Node ：在構建時,其實只需要message_generation,而在運行時,我們只需要message_runtime.

4.4 編譯package

Some new messages have been created,所以需要重新makeCheck out the package：

cd
cd catkin_ws
catkin_make

msg目錄中的任何.msg文件都將生成所有支持語言的代碼.

C++消息的頭文件將生成在~/catkin_ws/devel/include/beginner_tutorials/

python腳本將創建在~/catkin_ws/devel/lib/python2.7/dist-packages/beginner_tutorials/msg

5、msg命令實操

5.1 rosmsg list

rosmsg list 列出ROS中的所有消息（msg）.

5.2 rosmsg packages

rosmsg packages [options] List packages that contain messages.

# List packages that contain messages,Displays one package name per line
rosmsg packages
# List the packages containing the message on one line
rosmsg packages -s

5.3 rosmsg package

rosmsg package [package-name] List a package（package）的消息.

5.4 rosmsg show / rosmsg info

rosmsg show [message type] Displays the details of the message.

5.5 rosmsg md5

rosmsg md5[message type] 顯示md5加密的消息.If the compiled version does not match,This will also issue a warning.

Node：md5 Commands are intended for expert users only.（？？）

6、Practical programming – Topic communication sends custom messages

功能：Topic-based communication,The publisher publishes a custom message at a certain frequency and prints out the message,Subscribers subscribe to custom messages and print out messages.
實現：
1. 創建發布者（talker）節點,The node continuously broadcasts custom messages.
2. 創建訂閱者（listener）節點,The node continuously receives custom messages.
3. 創建自定義消息（Num.msg）,（見4.1小節 創建msg）
4. Publish and subscribe topicschatter

6.1 編寫程序（C++）

在beginner_tutorials軟件包的srcCreate publisher and subscriber source files in the directory：

roscd beginner_tutorials
cd src
touch talker.cpp listener.cpp

6.1.1 發布者程序（talker.cpp）

#include "ros/ros.h"
#include "beginner_tutorials/Num.h" // 在 /devel/include 目錄下
int main(int argc, char **argv)
{

/* 防止中文亂碼 */
setlocale(LC_ALL,"");
/* 初始化ROS節點 */
ros::init(argc, argv, "talker");
/* Create a handle for this process node */
ros::NodeHandle nh;
/* 創建發布者對象 */
ros::Publisher pub = nh.advertise<beginner_tutorials::Num>("chatter", 1000);
/* Sets the frequency of recurring releases to 1Hz */
ros::Rate loop_rate(1);
/* 要發布的消息 */
beginner_tutorials::Num msg;
msg.num = 0;
while(ros::ok())
{

ROS_INFO("當前num值為: %d",msg.num);
/* 發布消息 */
pub.publish(msg);
ros::spinOnce();
loop_rate.sleep();
msg.num += 1;
}
return 0;
}

Summarize the content above：
初始化ROS系統
Announce to the master node that we are going to be therechatter話題上發布beginner_tutorials/Num類型的消息
以每秒1times the speed directionchatterTopic cyclically publishes messages

6.1.2 訂閱者程序（listener.cpp）

#include "ros/ros.h"
#include "beginner_tutorials/Num.h" // 在 /devel/include 目錄下
/* 回調函數,當有新消息到達chatterIt will be called when the topic is reached */
void chatterCallback(const beginner_tutorials::Num::ConstPtr& msg)
{

ROS_INFO("receivedNum的值: %d",msg->num);
}
int main(int argc, char **argv)
{

/* 防止中文亂碼 */
setlocale(LC_ALL,"");
/* 初始化ROS節點 */
ros::init(argc, argv, "listener");
/* Create a handle for this process node */
ros::NodeHandle nh;
/* 創建訂閱者對象 * Subscribe via Node Managerchatter話題.收到消息,調用回調函數chatterCallback. * 第2The first parameter is the queue size,>1000時,Old messages are discarded. */
ros::Subscriber sub = nh.subscribe("chatter",1000, chatterCallback);
/* Start a self-loop 回調函數處理, 不占用太多CPU */
ros::spin();
return 0;
}

同樣地,我們來總結一下：
初始化ROS系統
訂閱chatter話題
開始spin自循環,等待消息的到達
當消息到達後,調用chatterCallback()函數

6.1.3 配置CMakeLists.txt

只需將這幾行添加到CMakeLists.txt文件的底部：

add_executable(talker src/talker.cpp)
target_link_libraries(talker ${catkin_LIBRARIES})
add_dependencies(talker ${PROJECT_NAME}_generate_messages_cpp)
add_executable(listener src/listener.cpp)
target_link_libraries(listener ${catkin_LIBRARIES})
add_dependencies(listener ${PROJECT_NAME}_generate_messages_cpp)

6.1.4 編譯、運行

編譯後,Execute the procedure in the terminal as shown below.

6.2 編寫程序（python）

在beginner_tutorials軟件包的scriptsCreate publisher and subscriber source files in the directory：

roscd beginner_tutorials
cd scripts
touch talker.py listener.py
chmod +x talker.py listener.py

6.2.1 發布者程序（talker.py）

#!/usr/bin/env python
# encoding: utf-8
import rospy
from beginner_tutorials.msg import Num
def talker():
# 初始化ROS節點
rospy.init_node("talker",anonymous=True)
# 創建發布者對象
pub = rospy.Publisher('chatter', Num, queue_size=1000)
# 創建一個Rate對象rate,1Hz
rate = rospy.Rate(1)
# 要發布的消息
msg = Num()
msg.num = 0
# 循環
while not rospy.is_shutdown():
rospy.loginfo("當前num值為: %d",msg.num)
pub.publish(msg)
rate.sleep()
msg.num += 1
if __name__ == '__main__':
try:
talker()
except rospy.ROSInterruptException:
pass

6.2.2 訂閱者程序（listener.py）

#!/usr/bin/env python
# encoding: utf-8
import rospy
from beginner_tutorials.msg import Num
def callback(msg):
rospy.loginfo("receivedNum的值: %d",msg.num)
def listener():
# 初始化ROS節點
rospy.init_node("listener",anonymous=True)
# 創建發布者對象
pub = rospy.Subscriber('chatter', Num, callback, queue_size=1000)
rospy.spin()
if __name__ == '__main__':
listener()

6.2.3 配置CMakeLists.txt

# 安裝python可執行腳本
catkin_install_python(PROGRAMS
scripts/turtle_publisher.py
scripts/talker.py
scripts/listener.py
DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
)

6.1.4 編譯、運行

編譯後,Execute the procedure in the terminal as shown below.

ROS.otg. ROS教程[EB/OL]. 2020-12-22[2022-7-5].
http://wiki.ros.org/cn/ROS/Tutorials. ︎
.ROS.org. 編寫簡單的發布者和訂閱者（C++）[EB/OL]. 2020-12-25[2022-07-30]. https://wiki.ros.org/cn/ROS/Tutorials/WritingPublisherSubscriber%28c%2B%2B%29. ︎
.ROS.org. 編寫簡單的發布者和訂閱者（Python）[EB/OL]. 2020-12-25[2022-07-30]. https://wiki.ros.org/cn/ROS/Tutorials/WritingPublisherSubscriber%28python%29. ︎
ROS.org. msg[EB/OL]. https://wiki.ros.org/msg[2022-07-30]. https://wiki.ros.org/msg.︎