How to create a 2D map of the environment#

🏁 Goal of this tutorial

By the end of this tutorial, you will know how to create a 2D map of the environment (AKA OccupancyGrid) using your robot.

Pre-requisites#

You should be able to remotely connect to your robot Set up ROS 2 communication with the robot.

You should be familiar with ROS’s RViz

You should be familiar with The startup process of the robot and application management

You should first have completed the How to teleoperate your robot

Start the SLAM#

By default, PAL Robots start in localization mode. To start mapping, you first need to stop the localization module with the command:

pal module stop localization

And then start the slam module with the command:

pal module start slam

Attention

Both the localization and the slam modules will publish a transform between the frames map and base_footprint. For this reason, you should not start both modules at the same time. When starting the slam module make sure you first shut down the localization module and vice-versa.

Otherwise, if you are using the simulated robot, you can refer to Simulation to learn how to start the SLAM.

Create a Map#

To visualize in real-time the map being created, you need to establish the communication with the robot as explained in Set up ROS 2 communication with the robot.

Then, in the same terminal that is connected to the robot, you can start RViz with the command:

rviz2 -d /opt/pal/$PAL_DISTRO/share/<ROBOT>_2dnav/config/rviz/navigation.rviz

Attention

Make sure to replace the <ROBOT> placeholder with the name of your robot (e.g. tiago, omni_base, tiago_pro, etc.).

You can now use any teleoperation methods described in the How to teleoperate your robot to move the robot around the environment and create the map. Alternatively, you can also make the robot move autonomously as described in How to Autonomously Navigate while avoiding obstacles. As the robot explores new areas of the environment, the map will be updated in real-time in RViz.

Save the Map#

Once you are satisfied with the created map, you can save it using the map_server CLI with the command:

ros2 run nav2_map_server map_saver_cli -t /map -f /home/pal/my_map --free 0.196 --occ 0.65

Alternatively, you can also save the map using the slam_toolbox RViz plugin:

Similarly, you can call the /slam_toolbox/save_map with the following command:

ros2 service call /slam_toolbox/save_map slam_toolbox/srv/SaveMap "name:
 data: '/home/pal/my_map'"

Attention

Make sure that the path you specify (e.g. /home/pal/) exists and is accessible.

Independently of the method you choose, in the specified directory (e.g. /home/pal/) two files will be created with the name you choose (e.g. my_map). The my_map.pgm file contains the map image, and the my_map.yaml file contains the map metadata used to load the map in ROS 2 and convert it to an OccupancyGrid message.

image: my_map.pgm
mode: trinary
resolution: 0.05
origin: [-13.9, -8.63, 0]
negate: 0
occupied_thresh: 0.65
free_thresh: 0.196

Next steps#

The map you created can be now used for the 📍 Localization of the robot. To learn how to use the newly created map for localization, you can refer to the How to Localize in a known map of the environment.

The map you created can also be used to create a new Building or extend an existing one. To learn how to create a new Building, you can refer to the 🚧 Tutorial: How to create and annotate your Environment.