Project AirSim ROS Bridge Examples: build_map¶

build_map demonstrates using the Project AirSim with the ROS MoveIt! motion package and the RViz visualizer to create a 3D occupancy map. This map indicates the parts of the world that are already occupied so no part of the robot may also occupy those areas. MoveIt’s 3D occupancy map uses the ROS OctoMap library which stores voxels in a 3D manner using a eight-way tree structure (an “octree”.)

In this example, the Project AirSim robot is configured with a LIDAR sensor and the 3D point cloud from the sensor is fed to MoveIt!’s Depth Image Octomap Updater plug-in to update the OctoMap in real time.

The robot is moved automatically using a “mission script”. At the end of the movements, the occupancy map is retrieved from MoveIt! and saved to a file.

Requirements¶

The build_map example requires the following:

A version of Python supported by the Project AirSim Client API.
The following Python packages in addition to those required by the Project AirSim ROS Bridge: moveit andmoveit_msgs.

Setup¶

See the setup for the Project AirSim ROS Bridge Examples.

Building¶

See the building the Project AirSim ROS Bridge Examples.

Running¶

Activate the Python virtual environment for Project AirSim.
Run Project AirSim.
Run the example with:

    roslaunch projectairsim_ros_examples build_map.launch

RViz will run to show the robot and the OctoMap as it is created. The robot will automatically launch, fly a path, return, and land. The example will then save the OctoMap to a file exit.

ROS parameters¶

The main launch file, build_map.launch, accepts several ROS arguments to help run the example in your environment. To pass an argument from the command-line, use the syntax “argument:=value” in the roslaunch command. For instance, to specify the IP address where AirSim is running:

    roslaunch projectairsim_ros_examples build_map.launch airsim_ip_address:=192.168.0.1

Argument	Value	Default	Description
`airsim_ip_address`	string	127.0.0.1	The IP address of the host running Project AirSim (e.g., `airsim_ip_address:=127.0.0.1`).
`sim_config_path`	string	(`projectairsim_ros_examples` package dir)../../../client/python/example_user_scripts/sim_config	The path to the directory containing the Project AirSim config files.

Technical description¶

This example uses MoveIt!’s Depth Image Octomap Updater plug-in to build the 3D occupancy map.

The build_map.py script creates the Project AirSim ROS Bridge node and loads the scene config file “scene_drone_sensors.jsonc” which configures the robot with multiple sensors including LIDAR. The script also runs a “mission script” to fly the robot around and exits when the drone returns to its launch point.

The configuration file config/sensors_lidar.yaml adds the PointCloud Octomap Updater plug-in to the MoveIt! group and points the plug-in to the robot’s LIDAR sensor data topic published by the Project AirSim ROS Bridge. This topic publishes PointCloud2 messages supported by the Octomap Updater plug-in. As the robot flies around, the Updater plug-in processes the LIDAR data and marks voxels in the occupancy map as occupied wherever a LIDAR point is within 100 meters of the vehicle.

For performance reasons the occupany map is configured with a resolution of 1.0 meter per voxel in sensor_manager.launch.xml.

In the meanwhile, RViz is running with the MoveIt! MotionPlanning plugin to display the drone and the occupancy map as it is updated.

When build_map.py is done flying the vehicle, it uses the OctoHandler class in common/octomap_handler.py to retrieve the occupancy map from MoveIt! and save it to a file. It does this by subscribing to the /move_group/monitored_planning_scene topic for one update. When the update message is received, it serializes the octomap in the message using the Python pickle module and saves it to a file.

The build_map.py node is marked “required” in the primary ROS launch file build_map.launch. When build_map.py completes the mission script and exits, roslaunch automatically shuts down the rest of the nodes.

3rd party attributions¶

example_externals/moveit_simple_controller_manager and example_externals/action_controller are derived from work by Benoit Courty, Alessio Tonioni, and Wel Selby. The original work may be found at https://github.com/benoit-cty/ROS-Autonomous-Quadcopter-Flight, and https://github.com/wilselby/ROS_quadrotor_simulator.