ROS无人机初始化GPS定位漂移误差，确保无人机稳定飞行

引言： 由于GPS在室外漂移的误差比较大，在长时间静止后启动，程序发布的位置可能已经和预期的位置相差较大，导致无法完成任务，尤其是气压计的数据不准，可能会导致无人机不能起飞或者一飞冲天。本文主要是在进行程序控制的时候，首先拿到最新的漂移误差，在此基础上进行程序控制，可以保证程序的稳定运行。

步骤一：创建订阅者订阅无人机的里程计信息

//创建一个Subscriber订阅者，订阅名为/mavros/local_position/odom的topic，注册回调函数local_pos_cb
ros::Subscriber local_pos_sub = nh.subscribe<nav_msgs::Odometry>("/mavros/local_position/odom", 10, local_pos_cb);

步骤二：创建相关变量，获取无人机的实时位置信息

这里定义了较多的变量，最重要的是位置和标志为，其余的可以自行设置

//定义变量，用于接收无人机的里程计信息
tf::Quaternion quat; 
double roll, pitch, yaw;
float init_position_x_take_off =0;
float init_position_y_take_off =0;
float init_position_z_take_off =0;
bool  flag_init_position = false;
nav_msgs::Odometry local_pos;

步骤三：定义回调函数，在回调函数中获取漂移值

//回调函数接收无人机的里程计信息
void local_pos_cb(const nav_msgs::Odometry::ConstPtr& msg)
{local_pos = *msg;if (flag_init_position==false && (local_pos.pose.pose.position.z!=0)){init_position_x_take_off = local_pos.pose.pose.position.x;init_position_y_take_off = local_pos.pose.pose.position.y;init_position_z_take_off = local_pos.pose.pose.position.z;flag_init_position = true;		    }tf::quaternionMsgToTF(local_pos.pose.pose.orientation, quat);	tf::Matrix3x3(quat).getRPY(roll, pitch, yaw);
}

注：启动这个控制节点后，或订阅最新的初始位置，并且通过标志为控制只订阅一次，这个值就是最新的漂移值

步骤四：发布目标点，一定要把获取到的初始漂移值加上，如下：

//发布期望位置信息
pose.pose.position.x =init_position_x_take_off + 0;
pose.pose.position.y =init_position_y_take_off + 0;
pose.pose.position.z =init_position_z_take_off + ALTITUDE;
local_pos_pub.publish(pose);

这里ALTITUDE是我宏定义的0.5，表明无人机飞0.5米高度即可。室外使用的话，最好高度设置大于1米

步骤五：整体代码如下：

//包含ROS和MAVROS相关头文件 
#include <string> 
#include <ros/ros.h>
#include <geometry_msgs/PoseStamped.h>
#include <mavros_msgs/CommandBool.h>
#include <mavros_msgs/SetMode.h>
#include <mavros_msgs/State.h>
#include <move_base_msgs/MoveBaseAction.h>
#include <actionlib/client/simple_action_client.h>
#include <std_msgs/Bool.h>
#include <geometry_msgs/TwistStamped.h>
#include <mavros_msgs/PositionTarget.h>
#include <cmath>
#include <tf/transform_listener.h>
#include <nav_msgs/Odometry.h>
#include <mavros_msgs/CommandLong.h>   
#include <string>
#include <geometry_msgs/Twist.h>#define ALTITUDE  0.5//定义变量，用于接收无人机的状态信息
mavros_msgs::State current_state;
void state_cb(const mavros_msgs::State::ConstPtr& msg);//定义变量，用于接收无人机的里程计信息
tf::Quaternion quat; 
double roll, pitch, yaw;
float init_position_x_take_off =0;
float init_position_y_take_off =0;
float init_position_z_take_off =0;
bool  flag_init_position = false;
nav_msgs::Odometry local_pos;
void local_pos_cb(const nav_msgs::Odometry::ConstPtr& msg);//回调函数接收无人机的状态信息
void state_cb(const mavros_msgs::State::ConstPtr& msg)
{current_state = *msg;
}//回调函数接收无人机的里程计信息
void local_pos_cb(const nav_msgs::Odometry::ConstPtr& msg)
{local_pos = *msg;if (flag_init_position==false && (local_pos.pose.pose.position.z!=0)){init_position_x_take_off = local_pos.pose.pose.position.x;init_position_y_take_off = local_pos.pose.pose.position.y;init_position_z_take_off = local_pos.pose.pose.position.z;flag_init_position = true;		    }tf::quaternionMsgToTF(local_pos.pose.pose.orientation, quat);	tf::Matrix3x3(quat).getRPY(roll, pitch, yaw);
}
int main(int argc, char **argv)
{//防止中文乱码setlocale(LC_ALL, "");//ROS节点初始化，节点名为offboard_single_positionros::init(argc, argv, "offboard_single_position");//创建节点句柄ros::NodeHandle nh;ros::Publisher local_pos_pub = nh.advertise<geometry_msgs::PoseStamped>("mavros/setpoint_position/local", 10);//创建一个Subscriber订阅者，订阅名为/mavros/state的topic，注册回调函数state_cbros::Subscriber state_sub = nh.subscribe<mavros_msgs::State>("mavros/state", 10, state_cb);//创建一个Subscriber订阅者，订阅名为/mavros/local_position/odom的topic，注册回调函数local_pos_cbros::Subscriber local_pos_sub = nh.subscribe<nav_msgs::Odometry>("/mavros/local_position/odom", 10, local_pos_cb);//创建一个服务客户端，连接名为/mavros/cmd/arming的服务，用于请求无人机解锁ros::ServiceClient arming_client = nh.serviceClient<mavros_msgs::CommandBool>("mavros/cmd/arming");//创建一个服务客户端，连接名为/mavros/set_mode的服务，用于请求无人机进入offboard模式ros::ServiceClient set_mode_client = nh.serviceClient<mavros_msgs::SetMode>("mavros/set_mode");//设置话题发布频率，需要大于2Hz，飞控连接有500ms的心跳包ros::Rate rate(20.0);//等待连接到飞控while(ros::ok() && !current_state.connected){ros::spinOnce();rate.sleep();}//设置无人机的期望位置geometry_msgs::PoseStamped pose;pose.pose.position.x =init_position_x_take_off + 0;pose.pose.position.y =init_position_y_take_off + 0;pose.pose.position.z =init_position_z_take_off + ALTITUDE;//send a few setpoints before startingfor(int i = 100; ros::ok() && i > 0; --i){local_pos_pub.publish(pose);ros::spinOnce();rate.sleep();}//定义客户端变量，设置为offboard模式mavros_msgs::SetMode offb_set_mode;offb_set_mode.request.custom_mode = "OFFBOARD";//定义客户端变量，请求无人机解锁mavros_msgs::CommandBool arm_cmd;arm_cmd.request.value = true;//记录当前时间，并赋值给变量last_requestros::Time last_request = ros::Time::now();while(ros::ok()){//请求进入OFFBOARD模式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 {//请求解锁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();}}if(fabs(local_pos.pose.pose.position.z- init_position_z_take_off -ALTITUDE)<0.2){	if(ros::Time::now() - last_request > ros::Duration(3.0)){break;}}//发布期望位置信息pose.pose.position.x =init_position_x_take_off + 0;pose.pose.position.y =init_position_y_take_off + 0;pose.pose.position.z =init_position_z_take_off + ALTITUDE;local_pos_pub.publish(pose);ros::spinOnce();rate.sleep();}   while(ros::ok()){pose.pose.position.x =init_position_x_take_off + 0;pose.pose.position.y =init_position_y_take_off + 0;pose.pose.position.z =init_position_z_take_off + ALTITUDE;                   local_pos_pub.publish(pose);ros::spinOnce();rate.sleep();}return 0;
}