Robot Footprints in Nav2 for ROS 2

Don’t forget to include a footprint in your Navigation 2 (Nav2) configuration file so that the local and global cost maps can properly account for the outline of the robot when it is attempting to avoid collisions. You need a footprint for both the local and global cost maps. My cost map parameters are store in a file called “nav2_params.yaml“, and within it there is a section for “local_costmap” and one for “global_costmap“. Here is snippet from the configuration file showing the footprint line for the local cost map for my robot.

local_costmap:
  local_costmap:
    ros__parameters:
      footprint: "[[-0.450, -0.215], [-0.450, 0.215], [0.235, 0.215], [0.235, -0.215]]"

And there is a similar “footprint” line in the global_costmap section.

The footprint value must be enclosed in quotes, has an outer pair of square brackets, and then is a list of x and y comma-separated coordinate pairs, each pair enclosed in square brackets and each bracketed pair separated by commas. Each x and y coordinate is a point in the base_link coordinate frame of the robot.

You don’t need to add a coordinate pair at the end back to the origin–it will be assumed. So a line segment from the last pair [0.235, -0.215] to first pair [-0.450, -0.215] is assumed in the above example.

If you’re rather, you can declare a circular outline for your robot instead. Using, e.g.,

robot_radius: 0.25 # The outline is a circle with radius 0.25 meters

You don’t nave to use the same foot print list or radius for both the local and global cost maps. You might, for instance, use a footprint list for the local cost map but a radius for the global cost map. The article referenced at the end of this post has a discussion about this.

Here is what the above footprint outline looks like in rviz2 when visualizing my robot (which is also showing LIDAR, SONAR and time-of-flight sensors and the local cost map). The lime-green square box in the center is the footprint.

See Setting Up The Robot’s Footprint for more information.