嘗試創建node,發佈topic和tf消息

1. 創建文件夾

在catkin_ws/src 下創建project文件夾

$ cd catkin_ws/src
$ catkin_create_pkg   my_first_pkg roscpp rospy std_msgs

之後在/src會生成一個文件夾my_first_pkg，內部有一個src文件夾和一個CMakeLists.txt和package.xml文件

2. 在/src/my_first_pkg/src下創建一個cpp文件，這裏叫my_odom.cpp

#include <ros/ros.h>
#include <tf/transform_broadcaster.h>
#include <nav_msgs/Odometry.h>

int main(int argc, char** argv){
  ros::init(argc, argv, "odometry_publisher");

  ros::NodeHandle n;
  ros::Publisher odom_pub = n.advertise<nav_msgs::Odometry>("myodom", 50);
  tf::TransformBroadcaster odom_broadcaster;

  double x = 0.0;
  double y = 0.0;
  double th = 0.0;

  double vx = 0.1;
  double vy = -0.1;
  double vth = 0.1;

  ros::Time current_time, last_time;
  current_time = ros::Time::now();
  last_time = ros::Time::now();

  ros::Rate r(1.0);
  while(n.ok()){

    ros::spinOnce();               // check for incoming messages
    current_time = ros::Time::now();

    //compute odometry in a typical way given the velocities of the robot
    double dt = (current_time - last_time).toSec();
    double delta_x = (vx * cos(th) - vy * sin(th)) * dt;
    double delta_y = (vx * sin(th) + vy * cos(th)) * dt;
    double delta_th = vth * dt;

    x += delta_x;
    y += delta_y;
    th += delta_th;

    //since all odometry is 6DOF we'll need a quaternion created from yaw
    geometry_msgs::Quaternion odom_quat = tf::createQuaternionMsgFromYaw(th);

    //first, we'll publish the transform over tf
    geometry_msgs::TransformStamped odom_trans;
    odom_trans.header.stamp = current_time;
    odom_trans.header.frame_id = "odom";
    odom_trans.child_frame_id = "base_footprint"//"base_link";

    odom_trans.transform.translation.x = x;
    odom_trans.transform.translation.y = y;
    odom_trans.transform.translation.z = 0.0;
    odom_trans.transform.rotation = odom_quat;

    //send the transform
    odom_broadcaster.sendTransform(odom_trans);

    //next, we'll publish the odometry message over ROS
    nav_msgs::Odometry odom;
    odom.header.stamp = current_time;
    odom.header.frame_id = "odom";

    //set the position
    odom.pose.pose.position.x = x;
    odom.pose.pose.position.y = y;
    odom.pose.pose.position.z = 0.0;
    odom.pose.pose.orientation = odom_quat;

    //set the velocity
    odom.child_frame_id = "base_link";
    odom.twist.twist.linear.x = vx;
    odom.twist.twist.linear.y = vy;
    odom.twist.twist.angular.z = vth;

    //publish the message
    odom_pub.publish(odom);

    last_time = current_time;
    r.sleep();
  }
}

3. 修改CMakeLists.txt和package.xml中的內容，添加編譯依賴文件（其中roscpp rospy std_msgs之前創建文件夾時自動添加了），添加編譯目標

CMakeLists.txt 中添加

//編譯依賴文件
find_package(catkin REQUIRED COMPONENTS
  roscpp
  rospy
  std_msgs
  tf
  nav_msgs
)

// 編譯目標
add_executable(my_odom src/my_odom.cpp)
target_link_libraries(my_odom ${catkin_LIBRARIES})

package.xml 中添加

  <build_depend>tf</build_depend>
  <build_depend>nav_msgs</build_depend>
  <build_export_depend>tf</build_export_depend>
  <build_export_depend>nav_msgs</build_export_depend>
  <exec_depend>tf</exec_depend>
  <exec_depend>nav_msgs</exec_depend>

4. catkin_make 編譯即可

$ cd ~/catkin_ws/
catkin_ws$ catkin_make