ros学习之topic实例1

参考自

https://sychaichangkun.gitbooks.io/ros-tutorial-icourse163/content/chapter6/6.2.html

这里写一个demo:,一个talker,发布gps的信息，一个listener来接收信息，并算出到原点的距离.

创建工作空间

makdir -p ~/catkin_ws/src
cd ~/catkin_ws/src
# 创建一个包叫topic_demo
catkin_create_pkg topic_demo roscpp rospy std_msgs

会发现已生自动生成了这些

.
└── topic_demo
    ├── CMakeLists.txt
    ├── include
    │   └── topic_demo
    ├── package.xml
    └── src

在package.xml里面除了基本的信息之外，以及注释掉的那些之外，就是这几行了

	<buildtool_depend>catkin</buildtool_depend>
  <build_depend>roscpp</build_depend>
  <build_depend>rospy</build_depend>
  <build_depend>std_msgs</build_depend>
  <build_export_depend>roscpp</build_export_depend>
  <build_export_depend>rospy</build_export_depend>
  <build_export_depend>std_msgs</build_export_depend>
  <exec_depend>roscpp</exec_depend>
  <exec_depend>rospy</exec_depend>
  <exec_depend>std_msgs</exec_depend>

没错这是一些依赖.

在 CMake*.txt里面也是除了

find_package(catkin REQUIRED COMPONENTS
  roscpp
  rospy
  std_msgs
)

其他的都是注释掉的.

创建自定义的msg消息类型

新建 msg/gps.mgs

string state
float32 x
float32 y

内容很好理解，即一个状态，一个坐标的xy,

修改package.xml

在package.xml中要 要加入 “定义编译” 和运行msg 所需要的，即

• message_generation
• message_runtime

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

修改完后如下

  <buildtool_depend>catkin</buildtool_depend>
  <buildtool_depend>message_generation</buildtool_depend>
  <build_depend>roscpp</build_depend>
  <build_depend>rospy</build_depend>
  <build_depend>std_msgs</build_depend>
  <build_export_depend>roscpp</build_export_depend>
  <build_export_depend>rospy</build_export_depend>
  <build_export_depend>std_msgs</build_export_depend>
  <exec_depend>roscpp</exec_depend>
  <exec_depend>rospy</exec_depend>
  <exec_depend>std_msgs</exec_depend>
  <exec_depend>message_runtime</exec_depend>

修改CMake*.txt

主要是以下几处

# 添加依赖
find_package(catkin REQUIRED COMPONENTS
  message_generation
  roscpp
  rospy
  std_msgs
)

# 添加msg文件
add_message_files(
   FILES
   gps.msg
   #Message2.msg
)

generate_messages(
   DEPENDENCIES
   std_msgs
 )

catkin_package(
#  INCLUDE_DIRS include
#  LIBRARIES topic_demo
  CATKIN_DEPENDS roscpp rospy std_msgs message_runtime
#  DEPENDS system_lib
)

include_directories(
 include
  ${catkin_INCLUDE_DIRS}
)

编写发布者talker.cpp

//引入ROS头文件
#include <ros/ros.h>

//引入自定义 ms*生的头文件
#include <topic_demo/gps.h>

int main(int argc, char **argv)
{
    //ros的初始化
    ros::init(argc, argv, "talker");
    //这里的前两个参数用来解析ros参数，第三个参数是这个节点的名字,这里叫talker

    //实例化句柄，初始化该node
    ros::NodeHandle nh;

    //声明自定义的gps 类型的msg, 并给初始值
    topic_demo::gps msg;
    msg.x = 1.0;
    msg.y = 1.0;
    msg.state = "working";

    //创建发布者的实例
    ros::Publisher pub = nh.advertise<topic_demo::gps>("gps_info", 1);

    //定义其发布的频率
    ros::Rate loop_rate(1.0);

    //循环发布msg
    int idx=1;
    while (ros::ok())
    {
        msg.x = 2.0 * msg.x;
        msg.y = 1.0 * msg.y;
        ROS_INFO("Talker: %d times: GPS: x = %.f, y = %.f", msg.x, msg.y);

        //发布消息
        pub.publish(msg);
        //根据前面定义的频率，进行sleep
        loop_rate.sleep();
        idx++;

    }
    return 0;
}

编写 接收者 listener.cpp

#include <ros/ros.h>
#include <topic_demo/gps.h>
#include <std_msgs/Float32.h>


//定义接收节点的回调函数

void gpsCallback(const topic_demo::gps::ConstPtr &msg){
    std_msgs::Float32 dis;
    dis.data = sqrt(pow(msg->x, 2) + pow(msg->y, 2));
    ROS_INFO("listener: dis to origin = %f, state: %s", dis.data, msg->state.c_str());

}

int main(int argc, char **argv){
    ros::init(argc, argv, "listener");
    ros::NodeHandle nh;
    ros::Subscriber sub = nh.subscribe("gps_info", 1, gpsCallback);
    ros::spin();
    return 0;

}