ROS入门3.2（实例1）

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#ROS #入门

本文围绕ROS的topic_demo实例展开，给出了talker.cpp、listener.cpp的代码，实现消息的发布与订阅，还展示了CmakeLists.txt和package.xml的配置内容，帮助开发者了解在ROS中如何进行消息通信及项目配置。

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实例：topic_demo

在这里插入图片描述 3.talker.cpp

//ROS头文件
#include <ros/ros.h>
//自定义msg产生的头文件
#include <topic_demo/gps.h>

int main(int argc, char **argv)
{
//用于解析ROS参数，第三个参数为本节点名
ros::init(argc, argv, “talker”);

//实例化句柄，初始化node
ros::NodeHandle nh;

//自定义gps msg
topic_demo::gps msg;
msg.x = 1.0;
msg.y = 1.0;
msg.state = “working”;

//创建publisher
ros::Publisher pub = nh.advertise<topic_demo::gps>(“gps_info”, 1);

//定义发布的频率
ros::Rate loop_rate(1.0);
//循环发布msg
while (ros::ok())
{
//以指数增长，每隔1秒更新一次
msg.x = 1.03 * msg.x ;
msg.y = 1.01 * msg.y;
ROS_INFO("Talker: GPS: x = %f, y = %f ", msg.x ,msg.y);
//以1Hz的频率发布msg
pub.publish(msg);
//根据前面定义的频率, sleep 1s
loop_rate.sleep();//根据前面的定义的loop_rate,设置1s的暂停
}

return 0;
}
4.listener.cpp

//ROS头文件
#include <ros/ros.h>
//包含自定义msg产生的头文件
#include <topic_demo/gps.h>
//ROS标准msg头文件
#include <std_msgs/Float32.h>

void gpsCallback(const topic_demo::gps::ConstPtr &msg)
{
//计算离原点(0,0)的距离
std_msgs::Float32 distance;
distance.data = sqrt(pow(msg->x,2)+pow(msg->y,2));
//float distance = sqrt(pow(msg->x,2)+pow(msg->y,2));
ROS_INFO(“Listener: Distance to origin = %f, state: %s”,distance.data,msg->state.c_str());
}

int main(int argc, char **argv)
{
ros::init(argc, argv, “listener”);
ros::NodeHandle n;
ros::Subscriber sub = n.subscribe(“gps_info”, 1, gpsCallback);
//ros::spin()用于调用所有可触发的回调函数。将进入循环，不会返回，类似于在循环里反复调用ros::spinOnce()。
ros::spin();
return 0;
}
5.CmakeLists.txt

cmake_minimum_required(VERSION 2.8.3)
project(topic_demo)

find_package(catkin REQUIRED COMPONENTS
message_generation
roscpp
rospy
std_msgs
)
add_message_files(
FILES
gps.msg
)

generate_messages(
DEPENDENCIES
std_msgs
)

catkin_package(

CATKIN_DEPENDS roscpp rospy std_msgs message_runtime
）

include_directories(
include
${catkin_INCLUDE_DIRS}
)

add_executable(talker src/talker.cpp )
#必须添加add_dependencies，否则找不到自定义的msg产生的头文件
add_dependencies(talker topic_demo_generate_messages_cpp)
target_link_libraries(talker ${catkin_LIBRARIES})

add_executable(listener src/listener.cpp )
add_dependencies(listener topic_demo_generate_messages_cpp)
target_link_libraries(listener ${catkin_LIBRARIES})

package.xml

<?xml version="1.0"?> topic_demo 0.0.0 The publish_subscribe_demo package

davidhan

BSD

<buildtool_depend>catkin</buildtool_depend>
<build_depend>message_generation</build_depend>
<build_depend>roscpp</build_depend>
<build_depend>rospy</build_depend>
<build_depend>std_msgs</build_depend>
<run_depend>roscpp</run_depend>
<run_depend>rospy</run_depend>
<run_depend>std_msgs</run_depend>
<run_depend>message_runtime</run_depend>