【ROS入门篇·三】ROS通讯架构-Topic
快速链接：【ROS入门篇】ROS学习简介
一、ROS中Topic通讯机制
Topic: 异步通讯机制，topic可以同时有多个subscribers，也可以有多个publishers；
Publisher: 向指定话题，发布对应类型的消息；
Sublisher: 订阅话题，一旦话题消息存在，调用回调函数对消息进行处理。
二、Publisher节点示例
- C++实现（古月居案例）
/**
* pub_demo.cpp, 发布turtle/cmd_vel话题，消息类型为geometry_msgs::Twist
*/
#include
#include
int main(int argc, char **argv)
{
// ROS节点初始化
ros::init(argc, argv, "pub_demo_node");
// 创建ROS节点句柄
ros::NodeHandle n_;
// 创建一个Publisher，发布turtle/cmd_vel话题，消息类型为geometry_msgs::Twist，队列长度为10
ros::Publisher pub_ = n_.advertise("/turtle1/cmd_vel", 10);
// 设置循环频率
ros::Rate loop_rate(10);
int count=0;
while(ros::ok())
{
// 初始化类型为geometry_msgs::Twist的消息
geometry_msgs::Twist vel_msg;
vel_msg.linear.x=0.5;
vel_msg.linear.z=0.2;
// 发布消息
pub_.publish(vel_msg);
ROS_INFO("Publish turtle velocity command[%0.2f m/s, %0.2f rad/s]", vel_msg.linear.x, vel_msg.linear.z);
// 按照循环频率执行
loop_rate.sleep();
}
return 0;
} -
修改CMakeLists.txt，配置可执行.cpp文件信息
三、Subscriber节点示例
- C++实现（古月居案例）
/**
* sub_demo.cpp, 订阅/turtle1/pose话题，消息类型为turtlesim::Pose
*/
#include
#include
void Callback(const turtlesim::Pose::ConstPtr& msg)
{
ROS_INFO("Turtle pose x: %0.6f, y: %0.6f", msg->x, msg->y);
}
int main(int argc, char **argv)
{
// ROS节点初始化
ros::init(argc, argv, "sub_demo_node");
// 创建ROS节点句柄
ros::NodeHandle n_;
// 创建一个Subscriber，订阅/turtle1/pose话题，消息类型为turtlesim::Pose，队列长度为10，注册回调函数Callback()
ros::Subscriber sub_ = n_.subscribe("/turtle1/Pose", 10, Callback);
// 主程序阻塞在这里，循环等待回调函数
ros::spin();
} - 修改CMakeLists.txt，配置可执行.cpp文件信息
四、自定义消息
- 生成.msg文件，放在msg文件夹内
- 修改CMakeLists.txt和Package.xml文件
/* .msg文件示例，定义了一个表示people的消息类型 */
string name
uint8 sex
uint8 age
uint8 unknow=0
uint8 male=1
uint8 female=2五、PubAndSub节点示例
- 同一节点内订阅一个话题，并发布一个话题
/**
* SubAndPub_demo.cpp
* 订阅/velodyne_points话题，消息类型为sensor_msgs::PointCloud2
* 发布/processed_velodyne_points话题，消息类型为sensor_msgs::PointCloud2
*/
#include
#include
#include
#include
#include
using namespace std;
class SubAndPub
{
private:
ros::NodeHandle n_;
ros::Publisher pub_;
ros::Subscriber sub_;
std::string frame_id_;
public:
SubAndPub();
void callback(const sensor_msgs::PointCloud2& velodyne_sub);
void pub_cloud(ros::Publisher pub_, const pcl::PointCloud::Ptr cloud_out);
};// End of class SubscribeAndPublish
SubAndPub::SubAndPub()
{
// Topic you want to publish
pub_ = n_.advertise("/processed_velodyne_points",1);
// Topic you want to subscribe
sub_ = n_.subscribe("/velodyne_points", 1, &SubAndPub::callback,this);
}
void SubAndPub::callback(const sensor_msgs::PointCloud2& cloud_in)
{
// do something with the input and generate the output...
frame_id_ = cloud_in.header.frame_id;
pcl::PointCloud::Ptr cloud (new pcl::PointCloud);
pcl::fromROSMsg(cloud_in,*cloud);
pub_cloud(pub_,cloud);
}
void SubAndPub::pub_cloud(ros::Publisher pub_, const pcl::PointCloud::Ptr cloud_out)
{
sensor_msgs::PointCloud2 out;
pcl::toROSMsg(*cloud_out,out);
out.header.frame_id = frame_id_;
pub_.publish(out);
}
int main(int argc, char **argv)
{
// Initiate ROS
ros::init(argc, argv, "SubAndPub_demo_node");
// Create an object of class SubscribeAndPublish that will take care of everything
SubAndPub velodyne;
ros::spin();
return 0;
} - 修改CMakeLists.txt和package.xml，配置可执行.cpp文件信息