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Microsoft AirSim (legacy)

Microsoft AirSim (legacy) is an open-source simulator for drones built on Unreal Engine, with built-in PX4 SITL integration.

Overview

Microsoft AirSim (legacy) provides an alternative simulation backend for AirStack, offering:

  • PX4 SITL integration - Native MAVLink lockstep with PX4 autopilot
  • Unreal Engine environments - Photorealistic scenes (UE 4.27)
  • Depth camera simulation - Used by DROAN for obstacle avoidance
  • Lightweight setup - Pre-built binary environments, no Omniverse required

Trade-offs vs Isaac Sim:

  • Simpler setup (no NVIDIA Omniverse)
  • PX4 integration via standard MAVLink (same as real hardware)
  • Archived project (no new features, but stable)
  • UE 4.27 only (older engine)

Quick Start

1. Download an environment

Download a pre-built environment from the AirSim Linux releases and extract it into simulation/ms-airsim/environments/:

cd simulation/ms-airsim
mkdir -p environments && cd environments
wget https://github.com/microsoft/AirSim/releases/download/v1.8.1/AbandonedPark.zip
unzip AbandonedPark.zip

2. Launch Microsoft AirSim (legacy) + Robot

airstack up --env-file overrides/ms-airsim.env

To build the images first:

airstack image-build --profile ms-airsim

The container runs 1 + 2*NUM_ROBOTS tmux windows: - Window 0: AirSim binary (Unreal Engine rendering) - Windows 1..N: one PX4 SITL instance per robot - Windows N+1..2N: one ROS 2 bridge node per robot (depth + stereo RGB + camera_info)

To attach to the tmux session:

airstack connect ms-airsim

A video is below:

Architecture

┌────────────────────────────────┐     ┌──────────────────────┐
│     MS-AirSim Container        │     │   Robot Container    │
│       (172.31.0.200)           │     │                      │
│                                │     │                      │
│   AirSim Binary (UE4)          │     │  MAVROS              │
│      ▲    │                    │     │    ▲                 │
│      │    │ TCP 4560+i         │     │    │                 │
│      │    ▼ (lockstep)         │     │    │                 │
│   PX4 SITL ×N ─── MAVLink UDP ─┼─────┼─► 24540+i/24580+i    │
│      ▲                         │     │    │                 │
│      │                         │     │    ▼                 │
│   Bridge Node ×N ─── ROS 2 DDS─┼─────┼─► Perception → DROAN │
│   (stereo RGB + depth + info)  │     │                      │
└────────────────────────────────┘     └──────────────────────┘
            airstack_network (172.31.0.0/24)

Data flow:

  1. AirSim simulates physics and renders stereo RGB + depth for each vehicle
  2. N PX4 SITL instances run in lockstep with AirSim via TCP (port 4560+i)
  3. MAVROS in the robot container connects to PX4 SITL via MAVLink UDP (offboard 24540+i, onboard 24580+i)
  4. Bridge nodes (one per robot) publish stereo RGB + depth + camera_info to ROS 2 topics
  5. disparity_expansion converts depth to disparity for DROAN

Configuration

settings.json

Located at simulation/ms-airsim/config/settings.json, mounted into the container at ~/Documents/AirSim/settings.json.

Key settings:

Setting Value Purpose
SimMode Multirotor Drone simulation
ClockType SteppableClock Lockstep with PX4
VehicleType PX4Multirotor PX4 SITL vehicle
TcpPort 4560 + i PX4 lockstep connection (per robot i)
ControlPortLocal 24540 + i AirSim MAVLink proxy local port (moved off 14540+i so it doesn't intercept PX4 ↔ MAVROS traffic)
ControlPortRemote 24580 + i AirSim MAVLink proxy remote port

settings.json is generated at container start from settings.json.j2 via generate_settings.py, which expands per-robot port offsets, spawn positions, and camera parameters.

Cameras

The default configuration is a forward-facing stereo pair (left + right) plus aligned depth:

Property Default .env override
Resolution 480×300 AIRSIM_CAM_WIDTH, AIRSIM_CAM_HEIGHT
FOV 110° AIRSIM_CAM_FOV
Baseline (2 × Y offset) 0.12 m AIRSIM_CAM_Y
Forward (X) offset 0.4 m AIRSIM_CAM_X
Pitch 0° AIRSIM_CAM_PITCH

Cameras are defined per vehicle in the generated settings.json under Vehicles.drone<i>.Cameras.

Bridge node parameters

Located at simulation/ms-airsim/ros_ws/src/ms_airsim_ros_bridge/config/bridge.yaml:

Parameter Default Description
ms_airsim_ip 127.0.0.1 AirSim API address (same container, so localhost)
publish_rate 15.0 Camera / depth publish rate (Hz)
robot_name robot_1 ROS 2 topic namespace (set per-instance by the entrypoint to robot_<i>)
clock_rate 50.0 /clock publish rate (Hz)

Environment variables

Variable Default Description
SIM_IP 172.31.0.200 Simulation container IP
MS_AIRSIM_ENV_DIR simulation/ms-airsim/environments Host path to extracted AirSim environment
MS_AIRSIM_BINARY_PATH /ms-airsim-env/LinuxNoEditor/Blocks.sh Path to binary inside container

Published ROS 2 Topics

Topic Type Description
/{robot_name}/sensors/front_stereo/left/image_rect sensor_msgs/Image Left RGB image
/{robot_name}/sensors/front_stereo/left/camera_info sensor_msgs/CameraInfo Left camera intrinsics
/{robot_name}/sensors/front_stereo/right/image_rect sensor_msgs/Image Right RGB image
/{robot_name}/sensors/front_stereo/right/camera_info sensor_msgs/CameraInfo Right camera intrinsics
/{robot_name}/sensors/front_stereo/depth sensor_msgs/Image Depth image (32FC1, meters)
/clock rosgraph_msgs/Clock Simulation clock from AirSim

Project status

Microsoft archived AirSim. For a maintained successor, see Project AirSim (UE5, new API — integration planned as a future AirStack feature).

Troubleshooting

Bridge can't connect to Microsoft AirSim (legacy):

  • Ensure the AirSim binary is running and settings.json is loaded
  • Check that ms_airsim_ip parameter matches where AirSim is running

No depth images:

  • Verify the camera name in settings.json matches bridge.yaml
  • Check AirSim console for rendering errors

MAVROS won't connect:

  • Verify SIM_IP=172.31.0.200 is set in .env (default)
  • Ensure PX4 SITL has started (check AirSim console for MAVLink messages)
  • Check port configuration: offboard=24540+i, onboard=24580+i