Navitation Demos
The navigation demos can be run on either the robot computer, or an offboard computer. This tutorial assumes you are using the simulation, but the launch files described in the Nav2, SLAM, and Localization sections can be used on a physical robot, too.
Make sure you have installed the simulator before starting this tutorial. Take a look at the installation guide for details.
The clearpath_nav2_demos package contains launch files and configurations for Nav2 and slam_toolbox demos. These are open source navigation packages that allow Clearpath robots to create maps and autonomously navigate.
To install the package, run:
sudo apt-get update
sudo apt-get install ros-jazzy-clearpath-nav2-demos
Nav2
Clearpath robots use the Nav2 stack for navigation. Nav2 is what sends velocity commands to the robot to make it drive autonomously. The stack relies on sensor data published by the robot to operate.
SLAM vs Localization
In order for the robot to determine where it is in the world it uses a map in combination with its sensor data (primarily its IMU and lidar sensors). This map can be provided in one of two ways: SLAM (Simultaneous Localization and Mapping), or Localization.
The SLAM and Localization implementations in the clearpath_nav2_demos package are intended to be
used in flat, indoor environents. We do not recommend using them to navigate through
unstructured, outdoor environments nor in indoor enviromnents with elevation changes and ramps.
SLAM
SLAM is used to generate a new map or to navigate through new environents. It uses the robot's lidar sensor to locate walls and other obstacles, building a map of the area as it explores. SLAM can also modify areas of the map dynamically, keeping track of mobile obstacles as well as static ones.
SLAM is useful for navigating new or changing environments, but is limited in that it can only navigate through areas of the map it has already explored.
Localization
Localization uses an existing map along with live odometry and laserscan data to determine the position and orientation of the robot on the given map. It does not update the map if any changes have been made to the environment, but it can avoid new obstacles when navigating. Because the map doesn't change, the robot can more reliably navigate across large areas within the map, taking more predictable paths to get from one location to another.
If you are working in simulation the clearpath_nav2_demos package
includes maps of
the warehouse simulation environment.
Prerequisites
To use the Nav2 demos your robot must be equipped with a 2D lidar. An IMU is also recommended, though many Clearpath robots include a built-in IMU that can be used.
For simplicity, this tutorial will use the simulator, but the nav2, SLAM, and localization launch files can be used on a physical robot too.