Map-Based Navigation

In this tutorial, you will learn about map-based navigation in ROS. You will be able to develop a ROS program in C++ and Python that will allow you to define goal locations for the robot and then send these goal locations to the navigation stack to execute the mission and head towards the goal. Note that it is possible to do so with rviz, but in this tutorial, you will be able to do this programmatically. You will also learn how to configure ros stage simulation to use a map of your choice and perform a navigation mission in the select map.

Tip

At the end of this tutorial, you will be able to:

  • Understand how map-based navigation is performed in ROS.
  • Develop a ROS program that defines goal locations programmatically and send them to the navigation stack
  • Configure the ROS stage Turtlebot simulator to use a particular map of interest
  • Use sound_play ROS package to play sound in a ROS application.

Background

The objective of this tutorial is to use a map of interest and request the robot to go to certain locations on that map. In the previous tutorial Building a Map with a Turtlebot, you already learned how to build a map with the Turtlebot. You will learn how to use such a map to program navigation missions for the robot. Remember that a map in ROS consists of two files, namely a .yaml file that contains information about the map, and a .pgm file that contains the map itself. In this tutorial, we are going to consider the following University floor map to develop our navigation example

../_images/psu.png

Figure 1. University Floor Map

Later on, as an exercise, you will use your own map to develop a navigation mission for your Turtlebot.

In the map of Figure 1, we identify four locations of interests namely, the Cafe area, Office1, Office2 and Office3. Other locations can also be defined, but we just used these representative four locations for illustration purposes. If we want to develop a ROS program that allow the robot to navigate to those locations, we first need to know what are the (x,y) coordinate of these locations onto the map. This is what will be explained later. Then, we use these coordinates to define a navigation mission that we submit to the robot’s navigation stack to execute it. Remember that any robot on ROS runs the move_base navigation stack which allow the robot to find a path towards a goal and execute the path following while avoiding obstacles. Refer to Navigation Stack Review for a refresher.

Tutorial Files

You can find the whole cpp and python files in our GitHub repository. They are located in src/turtlebot/navigation/map_navigation folder. In particular, we will use the launch file map_navigation_psu.launch that contains all the needed ROS nodes for this tutorial. Here is the content of the map_navigation_psu.launch file.

<launch>
      <include file="$(find gaitech_edu)/src/turtlebot/navigation/map_navigation/launch/turtlebot_stage_psu.launch"/>
     <node name="map_navigation" pkg="gaitech_edu" type="map_navigation_node" output="screen">
     </node>
     <node name="playing_sound_node" pkg="sound_play" type="soundplay_node.py" output="screen">
     </node>
</launch>

We observe that there are three nodes:

  • The first one includes the turtlebot_stage_psu.launch file, which starts-up the Turtlebot simulated robots in the stage simulator. This file initialize several parameters related to the inital position of the robot and the maps that will be used. Here is a partial snapshot of this file:
<launch>
  <arg name="base"       default="$(optenv TURTLEBOT_BASE kobuki)"/>  <!-- create, rhoomba -->
  <arg name="stacks"     default="$(optenv TURTLEBOT_STACKS hexagons)"/>  <!-- circles, hexagons -->
  <arg name="3d_sensor"  default="$(optenv TURTLEBOT_3D_SENSOR kinect)"/>  <!-- kinect, asus_xtion_pro -->

  <!-- Name of the map to use (without path nor extension) and initial position -->
  <arg name="map_file"       default=" $(find gaitech_edu)/src/maps/psu.yaml"/> <!-- psu -->
  <arg name="world_file"     default=" $(find gaitech_edu)/src/maps/stage/psu.world"/>
  <arg name="initial_pose_x" default="20.925"/>
  <arg name="initial_pose_y" default="11.925"/>
  <arg name="initial_pose_a" default="0.0"/>
   ...
   ...

You can observe that this launch files defines the map_file, that is the yaml file that defines the map that will be used by the navigation stack, and displayed by rviz. In addition, it defines the world_file that is world file that defines also a map used by the stage simulator. Furthermore, initial_pose_x and initial_pose_y define the initial location of the robot in terms of x-coordinate and y-coordinate respectively. How to determine this initale location and locations of interest will be described in details in the next section of this tutorial.

  • The second node if the map_navigation_node that is the ROS program that we are going to develop to make the robot travel to certain location of interest. The program is developed in the file map_navigation.cpp in C++ and map_navigation.py in python
  • the third node, is optional, and represent the sound_play node that allow to make sound notification in a ROS program.

Finding the Coordinates for Locations of Interest

The first thing you need to do is to find the location of the locations where you want the robot to go. These locations depends on the map size and resolutions. The easiest way to do so is to use rviz to visualize the map and then getting the coordinate using the 2D Pose Estimate button. Let us start the Turtlebot simulator with the University floor map as follow:

roslaunch gaitech_edu map_navigation_stage_psu.launch

The simulator will open. Try to arrange the stage simulation, rviz and the command terminal as in the following picture for better visibility:

../_images/turtlebot-simulation.png

Figure 2: Turtlebot Simulation Environment

Now, you want to find the coordinate of any location of interest. open another terminal and write

rostopic echo /amcl_pose

This command will display any new /amcl_pose, which is the ROS topic represents the location of the robot on the map. Now, click on 2D Pose Estimate button, then click on any location of interest on the map. Go back to the terminal where wrote rostopic echo /amcl_pose, and you will find the coordinate of the point select as in the following figure:

../_images/show-location.png

Figure 3: Finding the Location of Interest

Take note of the (x,y) coordinates for the Cafe and the three offices. They should be close to these values:

Cafe (15.50, 10.20)
Office1 (27.70,12.50)
Office2 (30.44,12.50)
Office3 (35.20,12.50)

The following video demonstrates the whole process.

Writing the navigation program

Now, we are ready to write a program that allows the robot to navigate to the goal location. Here is the snapshot of the code in C++:

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#include <ros/ros.h>
#include <move_base_msgs/MoveBaseAction.h>
#include <actionlib/client/simple_action_client.h>
#include "sound_play/sound_play.h"

std::string path_to_sounds;

/** function declarations **/
bool moveToGoal(double xGoal, double yGoal);
char choose();

/** declare the coordinates of interest **/
double xCafe = 15.50;
double yCafe = 10.20;
double xOffice1 = 27.70 ;
double yOffice1 = 12.50;
double xOffice2 = 30.44 ;
double yOffice2 = 12.50;
double xOffice3 = 35.20 ;
double yOffice3 = 13.50;

bool goalReached = false;
 int main(int argc, char** argv){
   ros::init(argc, argv, "map_navigation_node");
   ros::NodeHandle n;
   sound_play::SoundClient sc;
   ros::spinOnce();
   path_to_sounds = "/home/ros/catkin_ws/src/gaitech_edu/src/sounds/";

   char choice = 'q';
   do{
      choice =choose();
      if (choice == '0'){
         goalReached = moveToGoal(xCafe, yCafe);
      }else if (choice == '1'){
         goalReached = moveToGoal(xOffice1, yOffice1);
      }else if (choice == '2'){
         goalReached = moveToGoal(xOffice2, yOffice2);
      }else if (choice == '3'){
         goalReached = moveToGoal(xOffice3, yOffice3);
      }
      if (choice!='q'){
         if (goalReached){
            ROS_INFO("Congratulations!");
            ros::spinOnce();
            sc.playWave(path_to_sounds+"ship_bell.wav");
            ros::spinOnce();

         }else{
            ROS_INFO("Hard Luck!");
            sc.playWave(path_to_sounds+"short_buzzer.wav");
         }
      }
   }while(choice !='q');
   return 0;
}

The program structure is very simple. The user is requested to press a key, and based on his selection, the defined method moveToGoal(x,y) will be executed, where x and y define the coordinates of the locations of interest. Lines 13-20 define the location of points of interest that we determined in the last section Finding the Coordinates for Locations of Interest. Then, from lines 42-51, if the goal is successully reached, the program will display congratulations text message and will plan a ship_bell sound. Otherwise, it will display hard luck message and will play the short buzzer sound.

Now, let us focus more on how the method moveToGoal(x,y) is implemented. Here is the code.

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bool moveToGoal(double xGoal, double yGoal){

   //define a client for to send goal requests to the move_base server through a SimpleActionClient
   actionlib::SimpleActionClient<move_base_msgs::MoveBaseAction> ac("move_base", true);

   //wait for the action server to come up
   while(!ac.waitForServer(ros::Duration(5.0))){
      ROS_INFO("Waiting for the move_base action server to come up");
   }

   move_base_msgs::MoveBaseGoal goal;

   //set up the frame parameters
   goal.target_pose.header.frame_id = "map";
   goal.target_pose.header.stamp = ros::Time::now();

   /* moving towards the goal*/

   goal.target_pose.pose.position.x =  xGoal;
   goal.target_pose.pose.position.y =  yGoal;
   goal.target_pose.pose.position.z =  0.0;
   goal.target_pose.pose.orientation.x = 0.0;
   goal.target_pose.pose.orientation.y = 0.0;
   goal.target_pose.pose.orientation.z = 0.0;
   goal.target_pose.pose.orientation.w = 1.0;

   ROS_INFO("Sending goal location ...");
   ac.sendGoal(goal);

   ac.waitForResult();

   if(ac.getState() == actionlib::SimpleClientGoalState::SUCCEEDED){
      ROS_INFO("You have reached the destination");
      return true;
   }
   else{
      ROS_INFO("The robot failed to reach the destination");
      return false;
   }

}

Line 4 defines a client that is responsible for sending navigation goal request to the move_base server. In fact, the navigation stack of ROS has a MoveBaseAction action server that receives navigation goals request, and then finds a global path from the robot location to the goal location through the Global Path Planner, and once a path is found, it executes the path while avoiding obstacle through the Local Path Planner until it reaches the destination or fails to do so for any reason (like unexpected obstacle found on path).

Lines 7-8 will wait until it finds the action server and will not proceed longer until it makes sure that it is alive and will receive navigation requests. This is in fact a blocking instruction.

Line 11 defines a goal location and lines 13-25 specify the parameters of that location. It is easy to understand that lines 19-25 define the coordinates for the goal location. In particular the orientation component values expressed in quaternion refers to a heading equal to zero degrees.

Lines 14-15 are extremely important, in particular line 14. Line 14 goal.target_pose.header.frame_id = "map" specifies the reference frame for that location. In this example, it is specified as the map frame, which simply means that the coordinates will be considered in the global reference frame related to the map itself. In other words, it is the absolute position on the map. In case where the reference frame is set with respect to the robot, namely goal.target_pose.header.frame_id = "base_link" (like in this tutorial), the coordinate will have a completely other meaning. In fact, in this case the coordinate will represent the (x,y) coordinate with respect to robot base frame attached to the robot, so it is a relative position rather than a absolute position as in the case of using the map frame.

Note

For example, if we consider the following piece of code for the goal location (changes are highlighted):

   move_base_msgs::MoveBaseGoal goal;

   //set up the frame parameters
   goal.target_pose.header.frame_id = "base_link"; //or "base_footprint"
   goal.target_pose.header.stamp = ros::Time::now();

   /* moving towards the goal*/
   goal.target_pose.pose.position.x =  1.0;
   goal.target_pose.pose.position.y =  0;
   goal.target_pose.pose.position.z =  0.0;
   goal.target_pose.pose.orientation.x = 0.0;
   goal.target_pose.pose.orientation.y = 0.0;
   goal.target_pose.pose.orientation.z = 0.0;
   goal.target_pose.pose.orientation.w = 1.0;

In this case, goal location refers to the position that is one meter ahead of the robot (in front of the robot), so by executing this goal location, the robot will just move 1 meter in straight line. This is because the goal location is one meter in the x-axis (that is the front of the robot) with respect to the base_link frame attached to the robot.

Line 15 adds a timestamp to the goal location.

Line 28 sends the goal location request to the move_base action server, and wait for its execution as shown in line 31 (ac.waitForResult()). Note that this request is sychrounous, which means it will block until the result is sent back to the requesting client object. After it finishes, we can check if the goal succeded or failed and output a message to the user accordingly.

In what follow, we present the equivalent code in Python, which does exactly the same thing:

:linenos:

import rospy
import actionlib
from move_base_msgs.msg import MoveBaseAction, MoveBaseGoal
from math import radians, degrees
from actionlib_msgs.msg import *
from geometry_msgs.msg import Point
from sound_play.libsoundplay import SoundClient

class map_navigation():

  def choose(self):

    choice='q'

    rospy.loginfo("|-------------------------------|")
    rospy.loginfo("|PRESSE A KEY:")
    rospy.loginfo("|'0': Cafe ")
    rospy.loginfo("|'1': Office 1 ")
    rospy.loginfo("|'2': Office 2 ")
    rospy.loginfo("|'3': Office 3 ")
    rospy.loginfo("|'q': Quit ")
    rospy.loginfo("|-------------------------------|")
    rospy.loginfo("|WHERE TO GO?")
    choice = input()
    return choice

  def __init__(self):

    sc = SoundClient()
    path_to_sounds = "/home/ros/catkin_ws/src/gaitech_edu/src/sounds/"

    # declare the coordinates of interest
    self.xCafe = 15.50
    self.yCafe = 10.20
    self.xOffice1 = 27.70
    self.yOffice1 = 12.50
    self.xOffice2 = 30.44
    self.yOffice2 = 12.50
    self.xOffice3 = 35.20
    self.yOffice3 = 13.50
    self.goalReached = False
    # initiliaze
    rospy.init_node('map_navigation', anonymous=False)
    choice = self.choose()

    if (choice == 0):

      self.goalReached = self.moveToGoal(self.xCafe, self.yCafe)

    elif (choice == 1):

      self.goalReached = self.moveToGoal(self.xOffice1, self.yOffice1)

    elif (choice == 2):

      self.goalReached = self.moveToGoal(self.xOffice2, self.yOffice2)

    elif (choice == 3):

      self.goalReached = self.moveToGoal(self.xOffice3, self.yOffice3)

    if (choice!='q'):

      if (self.goalReached):
        rospy.loginfo("Congratulations!")
        #rospy.spin()

        sc.playWave(path_to_sounds+"ship_bell.wav")


       else:
        rospy.loginfo("Hard Luck!")
        sc.playWave(path_to_sounds+"short_buzzer.wav")

    while choice != 'q':
      choice = self.choose()
      if (choice == 0):

        self.goalReached = self.moveToGoal(self.xCafe, self.yCafe)

      elif (choice == 1):

        self.goalReached = self.moveToGoal(self.xOffice1, self.yOffice1)

      elif (choice == 2):

        self.goalReached = self.moveToGoal(self.xOffice2, self.yOffice2)

      elif (choice == 3):

        self.goalReached = self.moveToGoal(self.xOffice3, self.yOffice3)

      if (choice!='q'):

        if (self.goalReached):
          rospy.loginfo("Congratulations!")
          #rospy.spin()

          sc.playWave(path_to_sounds+"ship_bell.wav")

        else:
          rospy.loginfo("Hard Luck!")
          sc.playWave(path_to_sounds+"short_buzzer.wav")


  def shutdown(self):
        # stop turtlebot
        rospy.loginfo("Quit program")
        rospy.sleep()

  def moveToGoal(self,xGoal,yGoal):

      #define a client for to send goal requests to the move_base server through a SimpleActionClient
      ac = actionlib.SimpleActionClient("move_base", MoveBaseAction)

      #wait for the action server to come up
      while(not ac.wait_for_server(rospy.Duration.from_sec(5.0))):
              rospy.loginfo("Waiting for the move_base action server to come up")


      goal = MoveBaseGoal()

      #set up the frame parameters
      goal.target_pose.header.frame_id = "map"
      goal.target_pose.header.stamp = rospy.Time.now()

      # moving towards the goal*/

      goal.target_pose.pose.position =  Point(xGoal,yGoal,0)
      goal.target_pose.pose.orientation.x = 0.0
      goal.target_pose.pose.orientation.y = 0.0
      goal.target_pose.pose.orientation.z = 0.0
      goal.target_pose.pose.orientation.w = 1.0

      rospy.loginfo("Sending goal location ...")
      ac.send_goal(goal)

      ac.wait_for_result(rospy.Duration(60))

      if(ac.get_state() ==  GoalStatus.SUCCEEDED):
              rospy.loginfo("You have reached the destination")
              return True

      else:
              rospy.loginfo("The robot failed to reach the destination")
              return False

if __name__ == '__main__':
    try:

        rospy.loginfo("You have reached the destination")
        map_navigation()
        rospy.spin()

    except rospy.ROSInterruptException:
        rospy.loginfo("map_navigation node terminated.")

Playing sounds

To add some animation to this example, we used the ROS package sound_play which allows to play sound files. Observe that we included the C library for the sound plan in line 4 of the first code above. Furthermore, to be able to play sounds, it is necessary to start the ROS node, which was already done in the map_navigation_psu.launch. Without this node, no sound can be played.

In the program, we create a sound client with sound_play::SoundClient sc; and also we defined the absolute path to sound files with path_to_sounds = "/home/ros/catkin_ws/src/gaitech_edu/src/sounds/".

Then, we use the method sc.playWave(path_to_the_sound_file) to play a certain sound file. For example, in case of successul mission, the sound is played with sc.playWave(path_to_sounds+"ship_bell.wav");.

Testing the code

To test the above example, you simply need to execute the command

roslaunch gaitech_edu map_navigation_stage_psu.launch

Then, on the terminal command, you enter the location of your choice based on the selection menu and observe how the robot navigates to the goal location.

OR

You can run the nodes separately as follows:

roslaunch gaitech_edu turtlebot_stage_psu.launch
rosrun sound_play soundplay_node.py

Then for C++ run the following:

rosrun gaitech_edu map_navigation_node

For Python run the following:

python your_path/gaitech_edu/src/turtlebot/navigation/map_navigation/scripts/map_navigation.py

Congratulation! You now know how to program navigation mission for your simulated Turtlebot.

For a live explanation and testing of the code, watch the following video

Testing with Your Own Map on Simulation and Real Robot

It is easy to apply the navigation code on a real robot. However, you should deploy it using the map of the environment where you are going to run the experiments.

First, using the instructions of the Building a Map with a Turtlebot tutorial, create the map of your experimental environment.

Now, you need to make changes to the launch and world files to consider the information of the map of your environment. Follow these steps:

  • Step 1. Put the .yaml and .pgm map files in the src/maps/ folder. Let us assume they are called mymap.yaml and myamap.pgm.
  • Step 2. In the src/turtlebot/navigation/map_navigation/launch/ folder, make a copy of the two files map_navigation_stage_psu.launch and turtlebot_stage_psu.launch and give them other names, for example map_navigation_maymap.launch and turtlebot_stage_mymap.launch. We will use these two files to launch the simulator with your own map.
  • Step 3. In the new file, map_navigation_maymap.launch, change turtlebot_stage_psu.launch with turtlebot_stage_mymap.launch. This mean you will start the Turtlebot simulator with the parameters of your map. For this, you need to make the following changes to the turtlebot_stage_mymap.launch
  • Step 4. Change the name of the map and world files in turtlebot_stage_mymap.launch file as follow:
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<launch>
  <arg name="base"       default="$(optenv TURTLEBOT_BASE kobuki)"/>  <!-- create, rhoomba -->
  <arg name="stacks"     default="$(optenv TURTLEBOT_STACKS hexagons)"/>  <!-- circles, hexagons -->
  <arg name="3d_sensor"  default="$(optenv TURTLEBOT_3D_SENSOR kinect)"/>  <!-- kinect, asus_xtion_pro -->

  <!-- Name of the map to use (without path nor extension) and initial position -->
  <arg name="map_file"       default=" $(find gaitech_edu)/src/maps/mymap.yaml"/> <!-- psu -->
  <arg name="world_file"     default=" $(find gaitech_edu)/src/maps/stage/mymap.world"/>
  .....
  • Step 5. Now, you need to edit the file mymap.world file. This file is used by stage to display the map. In the folder, src/maps/stage/, Make a copy of psu.world, change its name to mymap.world and open it with gedit.
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...
floorplan
(
  name "mymap"
  bitmap "../mymap.pgm"
  size [ map_width map_length 0.0 ] #the real size in meters (from yaml, resolution*pixels)
  pose [ width_offset length_offset 0.0 0.0 ]
)

# throw in a robot
turtlebot
(
  pose [x_init y_init 0.0 0.0 ]
  name "turtlebot"
  color "red"
)
 .....

First, change `psu and psu.pgm in Lines 4 and 5 as shown. Line 4 assigns a name to the floor plan, and Line 5 refer to the map itself, in our case mymap.pgm. Finding the size is important. The size can be determined from two information from the yaml file, namely, the resolution and the pixel width and the pixel length. For example, in case of psu.yaml file, we have a resolution = 0.05 and from the pgm file, the image of the map has (837*477) (pixels^2). Multiplying by the resolution, we get the size of the map as (41.85 * 23.85) m^2. So,in the case of psu map, width_map = 41.85 m and length_map=23.85 m.

For the width and length offsets, we generally set them to the half of the width and length respectively, in this case will be (20.925, 11.925). Then you set the initial position of the robot of your choice. For this, you can choose any position that would not conflict with an obstacle.

In case of psu, we set the initial position to the center of the map (20.925, 11.925) as a choice. Other choices would also work.

  • Step 5. finally, make sure to put the same initial location in the file map_navigation_maymap.launch,
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<launch>
  <arg name="base"       default="$(optenv TURTLEBOT_BASE kobuki)"/>  <!-- create, rhoomba -->
  <arg name="stacks"     default="$(optenv TURTLEBOT_STACKS hexagons)"/>  <!-- circles, hexagons -->
  <arg name="3d_sensor"  default="$(optenv TURTLEBOT_3D_SENSOR kinect)"/>  <!-- kinect, asus_xtion_pro -->

  <!-- Name of the map to use (without path nor extension) and initial position -->
  <arg name="map_file"       default=" $(find gaitech_edu)/src/maps/mymap.yaml"/> <!-- psu -->
  <arg name="world_file"     default=" $(find gaitech_edu)/src/maps/stage/mymap.world"/>
  <arg name="initial_pose_x" default="x_init"/>
  <arg name="initial_pose_y" default="y_init"/>
  <arg name="initial_pose_a" default="0.0"/>

Now, you should be able to run the simulator with your own map.

Running on a real robot

To deploy on a real robot, you simply need to build a map as mentioned in the Building a Map with a Turtlebot tutorial and after saving the map on your Turtlebot’s PC bring-up your turtlebot robot, and then follow the previous steps to save some locations of interest. After that execute the following commands:

On your Turtlebot’s PC

roscore
roslaunch turtlebot_bringup minimal.launch
roslaunch turtlebot_navigation amcl_demo.launch map_file:=/your_path/your_map.yaml

On your Workstation

roslaunch turtlebot_rviz_launchers view_navigation.launch
rosrun sound_play soundplay_node.py

For Python run:

python your_path/gaitech_edu/src/turtlebot/navigation/map_navigation/scripts/map_navigation.py

For C++ run:

rosrun gaitech_edu map_navigation_node

In the latter case, You must make sure to have correctly configured your network settings as explained in the Network Configuration tutorial.

References

The following links are for more information about:

Review Questions and Activity

  • Question 1. What is the ROS topic that is used to find the location of the robot?
  • Question 2. Explain the difference between these two codes:

Code 1

move_base_msgs::MoveBaseGoal goal;
goal.target_pose.header.frame_id = "base_footprint";
goal.target_pose.header.stamp = ros::Time::now();
goal.target_pose.pose.position.x =  2.0;
goal.target_pose.pose.position.y =  0;
goal.target_pose.pose.position.z =  0.0;
goal.target_pose.pose.orientation.x = 0.0;
goal.target_pose.pose.orientation.y = 0.0;
goal.target_pose.pose.orientation.z = 0.0;
goal.target_pose.pose.orientation.w = 1.0;

Code 2

move_base_msgs::MoveBaseGoal goal;
goal.target_pose.header.frame_id = "map";
goal.target_pose.header.stamp = ros::Time::now();
goal.target_pose.pose.position.x =  2.0;
goal.target_pose.pose.position.y =  0;
goal.target_pose.pose.position.z =  0.0;
goal.target_pose.pose.orientation.x = 0.0;
goal.target_pose.pose.orientation.y = 0.0;
goal.target_pose.pose.orientation.z = 0.0;
goal.target_pose.pose.orientation.w = 1.0;
  • Question 3. Consider the following yaml for a map.
image: /tmp/my_map.pgm
resolution: 0.050000
origin: [0.00000, 0.00000, 0.000000]
negate: 0
occupied_thresh: 0.65
free_thresh: 0.196

Given that my_map.pgm has the size 540x680 pixels, what is the size in meters for the environment?