Move With PID

 void trackCallback (const geometry_msgs::Point::ConstPtr & track_msg)
 {
   ros::NodeHandle nh;
   geometry_msgs::Twist move_msg;
   geometry_msgs::Point plot_msg;
   ros::Time time = ros::Time::now();
   double effort = 0;

   // Set the turn - turn on the z axis
   move_msg.linear.x = 0;
   move_msg.linear.y = 0;
   move_msg.linear.z = 0;
   move_msg.angular.x = 0;
   move_msg.angular.y = 0;

   // PID update
   effort = pid.updatePid(track_msg->x - MID_X, time - last_time);
   move_msg.angular.z = -effort / SCALE *  MAX_POWER;
   if (move_msg.angular.z >  MAX_POWER) move_msg.angular.z =  MAX_POWER;  
   if (move_msg.angular.z < -MAX_POWER) move_msg.angular.z = -MAX_POWER;  

   // Execute turn
   mover.publish(move_msg);

   // debug output
   plot_msg.x = track_msg->x - MID_X;
   plot_msg.y = - effort;
   plot_msg.z = move_msg.angular.z;
   plot.publish(plot_msg);

   // Debugging Output
   /*
   ROS_INFO("error: %f    effort: %f\n", track_msg->x - MID_X, effort);
   ROS_INFO("trackCallback x: %d  y: %d  radius: %d    result: %f",

(int)track_msg->x, (int)track_msg->y, (int)track_msg->z,

            move_msg.angular.z);
   */
 }