2.1、ROS+PX4仿真---定点飞行控制

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引言：本小节是在已经安装好仿真环境的情况下进行。仿真环境的安装可以参考视频讲解：链接如下

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​​环境安装和定点飞行代码详解​​

视频从小海龟例程开始，详细阐述了话题的订阅和发布，后续分析了本小节代码

​​视频：代码详解​​

1、进入到Firmware文件夹下，启动gazebo仿真环境：

make px4_sitl_default gazebo

2、启动MAVROS仿真

`roslaunch mavros px4.launch fcu_url:="udp://:14540@127.0.0.1:14557"`

3、启动飞行节点

rosrun offboard_node offboard_node

4、代码注释：

//相关头文件包含
#include <ros/ros.h>
#include <geometry_msgs/PoseStamped.h>
#include <mavros_msgs/CommandBool.h>
#include <mavros_msgs/SetMode.h>
#include <mavros_msgs/State.h>
 
mavros_msgs::State current_state;

//回调函数
void state_cb(const mavros_msgs::State::ConstPtr& msg){
    current_state = *msg;
}
 
int main(int argc, char **argv)
{
        //初始化节点
    ros::init(argc, argv, "offb_node");
    //创建节点句柄
    ros::NodeHandle nh;
        //创建订阅者，订阅话题mavros/state
    ros::Subscriber state_sub = nh.subscribe<mavros_msgs::State>
            ("mavros/state", 10, state_cb);
    //创建一个发布者，发布"mavros/setpoint_position/local"话题
    ros::Publisher local_pos_pub = nh.advertise<geometry_msgs::PoseStamped>
            ("mavros/setpoint_position/local", 10);
    //创建一个客户端，该客户端用来请求PX4无人机的解锁         
    ros::ServiceClient arming_client = nh.serviceClient<mavros_msgs::CommandBool>
            ("mavros/cmd/arming");
    //创建一个客户端，该客户端用来请求进入offboard模式
    ros::ServiceClient set_mode_client = nh.serviceClient<mavros_msgs::SetMode>
            ("mavros/set_mode");
 
    //搭配rate.sleep()函数，实现20Hz频率的循环;
    ros::Rate rate(20.0);
 
    // 等待飞控连接
    while(ros::ok() && !current_state.connected){
        ros::spinOnce();
        rate.sleep();
    }
 
      //创建一个变量，该变量是无人机即将起飞到的位置，相对于无人机上电时刻作为起始点
    geometry_msgs::PoseStamped pose;
    pose.pose.position.x = 0;
    pose.pose.position.y = 0;
    pose.pose.position.z = 2;
    
    //预发布期望位置信息，给无人机目标点
    //send a few setpoints before starting
    for(int i = 100; ros::ok() && i > 0; --i){
        local_pos_pub.publish(pose);
        ros::spinOnce();
        rate.sleep();
    }
   
    //设置客户端请求无人机进入“OFFBOARD”模式
    mavros_msgs::SetMode offb_set_mode;
    offb_set_mode.request.custom_mode = "OFFBOARD";
   
    //设置客户请无人机解锁
    mavros_msgs::CommandBool arm_cmd;
    arm_cmd.request.value = true;
 
      //获取时间戳
    ros::Time last_request = ros::Time::now();
 
    while(ros::ok()){
        //if语句循环请求进入OFFBOARD模式，进入以后则会进入else语句请求对无人机解锁。
        if( current_state.mode != "OFFBOARD" &&
            (ros::Time::now() - last_request > ros::Duration(5.0))){
            if( set_mode_client.call(offb_set_mode) &&
                offb_set_mode.response.mode_sent){
                ROS_INFO("Offboard enabled");
            }
            last_request = ros::Time::now();
        } else {
            if( !current_state.armed &&
                (ros::Time::now() - last_request > ros::Duration(5.0))){
                if( arming_client.call(arm_cmd) &&
                    arm_cmd.response.success){
                    ROS_INFO("Vehicle armed");
                }
                last_request = ros::Time::now();
            }
        }
       
        //循环发布期望位置信息，20Hz频率
        local_pos_pub.publish(pose);
 
        ros::spinOnce();
        rate.sleep();
    }
    return 0;
}