Ubuntu Linux for Robotics · Lesson 78 of 96

Costmaps

Global and local costmaps, layers, inflation and inspecting them in RViz2.

Estimated time · 45–75 min

Learning goals

What you will understand

Explain costmaps in your own words
Use it in a small workstation example
Verify the result instead of assuming it worked

Understand the idea first

The mental model

Costmaps turn the map and live sensor data into costs the planners use. The global costmap covers the whole map; the local costmap is a small window around the robot. Layers combine: static (from the map), obstacle (from sensors) and inflation (a safety margin around obstacles).

Set the robot radius or footprint, the resolution and the inflation radius in the Nav2 parameter YAML. View costmaps in RViz2 by adding a Map display for /global_costmap/costmap and /local_costmap/costmap. Too large an inflation radius blocks narrow corridors; too small lets the robot scrape walls.

Guided lesson

Work through these steps

1.
Open a terminal and record the current state before changing anything.
2.
Read the costmaps commands and predict what each one does.
3.
Run the commands one at a time and compare each output with your prediction.
4.
Write the commands that worked in a setup note you can repeat later.

Worked example

Read it before you run it

ros2 param get /global_costmap/global_costmap robot_radius
# Read the robot radius used by the global costmap.
ros2 param get /local_costmap/local_costmap width
# Read the local window width.
ros2 param set /global_costmap/global_costmap inflation_layer.inflation_radius 0.55
# Try a different inflation radius while running.
ros2 topic hz /local_costmap/costmap
# Check how often the local costmap updates.
ros2 service call /global_costmap/clear_entirely_global_costmap nav2_msgs/srv/ClearEntireCostmap
# Clear the global costmap.

What the example is doing

1.Lines without sudo only inspect or change files you own; sudo authorizes a system-wide change.
2.Read command output before moving to the next line. Stop if names, versions, disks, or paths differ from the lesson.
3.Comments beginning with # explain safety checks and are not executed by the shell.

Watch it run · Mobile robot

See what this code does

The terminal types this lesson's practice solution and runs it. The scene shows the kind of robot behaviour that code drives. It plays by itself and loops.

Practice code

Now type it yourself

Open a terminal, run the starter line by line (or save it as practice.sh and run bash practice.sh), and replace every TODO with your own command.

# TODO: read the parameter robot_radius of the global costmap node

Expected output

Double value is: 0.22

Stuck? Show the full solution (try it yourself first)

ros2 param get /global_costmap/global_costmap robot_radius

Expected result

How you know it worked

Each command completes without an unexplained error.
Your notes contain the command, the important output, and what it proves.

Practical exercise

Apply the lesson

View both costmaps in RViz2, change the inflation radius from 0.3 to 0.8 m, and describe how paths change in a narrow corridor.

Before you continue

You recorded the starting state
Every command and output is understood
The change can be repeated from your notes

If something goes wrong

A command says permission denied.

Check ownership and permissions first. Do not add sudo unless the command changes a documented system location.

A command or package is not found.

Check spelling, Ubuntu version, enabled repositories, and whether the previous installation command succeeded.