树莓派控制无人机实现定点降落（四）——gazebo无人机定点降落仿真环境搭建

1、编译px4_sitl_default

#在Firmware路径下
sudo make px4_sitl_default

  这个是用于仿真的，而px4_fmu-v5_default可以不编译，但如果没有它的话就需要用实物pixhawk连接电脑然后用mavros连接用于仿真，如果有它的话就不需要接自己的飞控，已经有虚拟飞控了。

2、编译gazebo

在Firmware/Tools/sitl_gazebo路径下执行:  

mkdir Build
### 将以下所有的[]都替换成Firmware所在的路径
### 设置插件的路径以便 Gazebo 能找到模型文件 
export GAZEBO_PLUGIN_PATH=${GAZEBO_PLUGIN_PATH}:[]/Tools/sitl_gazebo/Build
### 设置模型路径以便 Gazebo 能找到机型 
export GAZEBO_MODEL_PATH=${GAZEBO_MODEL_PATH}:[]/Tools/sitl_gazebo/models
### 禁用在线模型查找 
export GAZEBO_MODEL_DATABASE_URI="" 
### 设置 sitl_gazebo 文件夹的路径 
export SITL_GAZEBO_PATH=[]/Tools/sitl_gazebo
### 编译gazebo仿真
cd Build
cmake ..
make

3、仿真

cd src/Firmware
make posix_sitl_default
export FIRMWARE_DIR=[]//[]里添加firmware的路径
source ~/catkin_ws/devel/setup.bash    // 只有mavros是用源码编译的才需要
source Tools/setup_gazebo.bash $(FIRMWARE_DIR) $(FIRMWARE_DIR)/build/px4_sitl_default
export ROS_PACKAGE_PATH=$ROS_PACKAGE_PATH:$(FIRMWARE_DIR)
export ROS_PACKAGE_PATH=$ROS_PACKAGE_PATH:$(FIRMWARE_DIR)/Tools/sitl_gazebo
roslaunch px4 mavros_posix_sitl.launch

  在执行roslaunch之后将会看到仿真界面就成功了。  
  为了之后方便可以直接把需要配置的环境加到~/.bashrc里：  

sudo vim ~/.bashrc

#在最后添加
export FIRMWARE_DIR=[]//[]里添加firmware的路径
export GAZEBO_PLUGIN_PATH=${GAZEBO_PLUGIN_PATH}:$FIRMWARE_DIR/Tools/sitl_gazebo/build
source $FIRMWARE_DIR/Tools/setup_gazebo.bash $FIRMWARE_DIR $FIRMWARE_DIR/build/px4_sitl_default
export ROS_PACKAGE_PATH=$ROS_PACKAGE_PATH:$FIRMWARE_DIR
export ROS_PACKAGE_PATH=$ROS_PACKAGE_PATH:$FIRMWARE_DIR/Tools/sitl_gazebo

  至此gazebo环境就搭建好了。 在命令行的pxh处输入command takeoff可以让它起飞，飞至两米高度，五秒后降落。

3、尝试offboard_node

按照px4官网的方法可以建立一个offboard_node来控制它起飞，方法如下：  

#创建包
mkdir -p ~/catkin_ws/src
cd ~/catkin_ws/src
catkin_create_pkg offb roscpp mavros
cd ~/catkin_ws/src/offb/src
vim offb_node.cpp

  在文件中复制粘贴  

/**
 * @file offb_node.cpp
 * @brief offboard example node, written with mavros version 0.14.2, px4 flight
 * stack and tested in Gazebo SITL
 */
 
#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;
void state_cb(const mavros_msgs::State::ConstPtr& msg){
    current_state = *msg;
}
 
int main(int argc, char **argv)
{
    ros::init(argc, argv, "offb_node");
    ros::NodeHandle nh;
 
    ros::Subscriber state_sub = nh.subscribe<mavros_msgs::State>
            ("mavros/state", 10, state_cb);
    ros::Publisher local_pos_pub = nh.advertise<geometry_msgs::PoseStamped>
            ("mavros/setpoint_position/local", 10);
    ros::ServiceClient arming_client = nh.serviceClient<mavros_msgs::CommandBool>
            ("mavros/cmd/arming");
    ros::ServiceClient set_mode_client = nh.serviceClient<mavros_msgs::SetMode>
            ("mavros/set_mode");
 
    //the setpoint publishing rate MUST be faster than 2Hz
    ros::Rate rate(20.0);
 
    // wait for FCU connection
    while(ros::ok() && current_state.connected){
        ros::spinOnce();
        rate.sleep();
    }
 
    geometry_msgs::PoseStamped pose;
    pose.pose.position.x = 0;
    pose.pose.position.y = 0;
    pose.pose.position.z = 2;
 
    //send a few setpoints before starting
    for(int i = 100; ros::ok() && i > 0; --i){
        local_pos_pub.publish(pose);
        ros::spinOnce();
        rate.sleep();
    }
 
    mavros_msgs::SetMode offb_set_mode;
    offb_set_mode.request.custom_mode = "OFFBOARD";
 
    mavros_msgs::CommandBool arm_cmd;
    arm_cmd.request.value = true;
 
    ros::Time last_request = ros::Time::now();
 
    while(ros::ok()){
        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();
            }
        }
 
        local_pos_pub.publish(pose);
 
        ros::spinOnce();
        rate.sleep();
    }
 
    return 0;
}

  （代码有pixhawk官网给出） 在CmakeLists中添加  

add_executable(offb_node src/offb_node.cpp)

  之后回到catkin_ws路径catkin_make编译然后rosrun offb offb_node即可看到无人机起飞到两米处。

4、无人机添加单目相机

修改launch文件： 在Firmware/launch文件下的mavros_posix_sitl.launch文件，添加一句：  

<arg name="cam" default="iris_fpv_cam"/>

  之后将  

<arg name="sdf" default="$(find mavlink_sitl_gazebo)/models/$(arg vehicle)/$(arg vehicle).sdf"/>

  改为  

<arg name="sdf" default="$(find mavlink_sitl_gazebo)/models/$(arg cam)/$(arg cam).sdf"/>

  这样就可以了，再次执行roslaunch px4 mavros_posix_sitl.launch可以看到无人机有了前置摄像头，画面将发布到/iris/usb_cam/image_raw话题，可以通过rqt查看。 改变摄像头姿态： 打开Firmware/Tools/sitl_gazebo/models/iris_fpv_cam/iris_fpv_cam.sdf文件修改pose标签即可，改为0 0 0 0 1.57 0便是下视摄像头。