text: #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>("odom", 1000);
    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_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();
    }
  }
  