ROS学习笔记（四）: publisher的编程实现

四、publisher的编程实现

1、在工作区创建功能包

目的：创建一个使小乌龟画圆的publisher

打开工作区

cd ~/catkin_ws/src

创建工作包，不要使用大写字母命名，会编译不成功。。。

catkin_create_pkg learning_topic roscpp rospy std_msgs geometry_msgs turtlesim

2、创建publisher代码

实现publisher一般有以下步骤：

• 初始化ROS节点
• 向ROS Master注册节点信息，包括发布的话题名和话题中的消息类型
• 创建消息数据
• 按照一定频率循环发布数据

首先，在learning_topic/src目录下创建publisher代码

cd learning_topic/src
sudo gedit velocity_publisher.cpp

/**
 * 该publisher将发布turtler1/cmd_vel话题，消息类型geometry_msgs::Twist
**/

#include 
#include 

int main(int argc, char **argv)
{
	// ROS节点初始化
	ros::init(argc, argv, "velocity_publisher");

	// 创建节点句柄
	ros::NodeHandle n;

	// 创建一个Publisher，发布名为/turtle1/cmd_vel的topic，消息类型为geometry_msgs::Twist，队列长度10
	ros::Publisher turtle_vel_pub = n.advertise("/turtle1/cmd_vel", 10);

	// 设置循环的频率
	ros::Rate loop_rate(10);

	//int count = 0;
	while (ros::ok())
	{
	    // 初始化geometry_msgs::Twist类型的消息
		geometry_msgs::Twist vel_msg;
		// 小乌龟的
		vel_msg.linear.x = 0.5;
		vel_msg.angular.z = 0.2;

	    // 发布消息
		turtle_vel_pub.publish(vel_msg);
        count +=1;
		ROS_INFO("Publsh turtle velocity command[%0.2f m/s, %0.2f rad/s]", 
				vel_msg.linear.x, vel_msg.angular.z);

	    // 按照循环频率延时
	    loop_rate.sleep();
	}

	return 0;
}

3、配置publisher代码编译规则

打开CMakeLists.txt

cd ~/catkin_ws/src/learning_topic 
sudo gedit CMakeLists.txt

添加下列代码

## 设置需要编译的代码和生成的可执行文件
# velocity_punlisher.cpp是需要编译的代码，velocity_publisher是生成的可执行文件
add_executable(velocity_publisher src/velocity_publisher.cpp)
## 设置链接库
target_link_libraries(velocity_publisher ${catkin_LIBRARIES})

4、编译并运行publisher

cd ~/catkin_ws
catkin_make 

成功编译

Base path: /home/doublehuhu/catkin_ws
Source space: /home/doublehuhu/catkin_ws/src
Build space: /home/doublehuhu/catkin_ws/build
Devel space: /home/doublehuhu/catkin_ws/devel
Install space: /home/doublehuhu/catkin_ws/install
####
#### Running command: "make cmake_check_build_system" in "/home/doublehuhu/catkin_ws/build"
####
-- Using CATKIN_DEVEL_PREFIX: /home/doublehuhu/catkin_ws/devel
-- Using CMAKE_PREFIX_PATH: /opt/ros/melodic
-- This workspace overlays: /opt/ros/melodic
-- Found PythonInterp: /usr/bin/python2 (found suitable version "2.7.17", minimum required is "2") 
-- Using PYTHON_EXECUTABLE: /usr/bin/python2
-- Using Debian Python package layout
-- Using empy: /usr/bin/empy
-- Using CATKIN_ENABLE_TESTING: ON
-- Call enable_testing()
-- Using CATKIN_TEST_RESULTS_DIR: /home/doublehuhu/catkin_ws/build/test_results
-- Found gtest sources under '/usr/src/googletest': gtests will be built
-- Found gmock sources under '/usr/src/googletest': gmock will be built
-- Found PythonInterp: /usr/bin/python2 (found version "2.7.17") 
-- Using Python nosetests: /usr/bin/nosetests-2.7
-- catkin 0.7.19
-- BUILD_SHARED_LIBS is on
-- BUILD_SHARED_LIBS is on
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- ~~  traversing 1 packages in topological order:
-- ~~  - learning_topic
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- +++ processing catkin package: 'learning_topic'
-- ==> add_subdirectory(learning_topic)
-- Configuring done
-- Generating done
-- Build files have been written to: /home/doublehuhu/catkin_ws/build
####
#### Running command: "make -j2 -l2" in "/home/doublehuhu/catkin_ws/build"
####
Scanning dependencies of target velocity_publisher
[ 50%] Building CXX object learning_topic/CMakeFiles/velocity_publisher.dir/src/velocity_publisher.cpp.o
[100%] Linking CXX executable /home/doublehuhu/catkin_ws/devel/lib/learning_topic/velocity_publisher
[100%] Built target velocity_publisher

配置zsh

source devel/setup.zsh 

运行roscore

roscore

打开新终端

rosrun turtlesim turtlesim_node 

回车，出现小乌龟，再打开一个新终端，运行新写好的publisher

rosrun learning_topic velocity_publisher

出现错误，找不到功能包？

[rospack] Error: package 'learning_topic' not found

于是试着打开工作区，重新运行写好的publisher

cd ~/catkin_ws
rosrun learning_topic velocity_publisher

依然出现错误

[rospack] Error: package 'learning_topic' not found

试着再次执行以下执行：

source devel/setup.zsh 

运行写好的publisher

rosrun learning_topic velocity_publisher

小乌龟成功画圆！