Using a Vicon indoor positioning system

Overview

Robotics labs commonly have an indoor flying facility using a Vicon indoor positioning system. These systems use infra-red cameras to give a high rate (200Hz) position and attitude information via a network connection.

The Vicon system comes with a SDK that provides APIs for accessing the Vicon positioning data. To use the Vicon data with ArduPilot, you need a tool which can use this API and reformats the data into MAVlink format. This can be done by manipulating the MAVlink packet “GPS_INPUT”, creating a pseudo GPS source for ArduPilot.

Hardware Setup

The following hardware is used in this guide:

  • Vicon camera system with a Host PC

  • Vicon Calibration Wand

  • Linux laptop (GCS) with both Wi-Fi and Ethernet capability

  • Pixhawk6C flight controller

  • ESP8266 Wi-Fi module

  • Conventional Radio controller and receiver

  • Minimum of 4 reflective IR markers per drone

  • Ethernet cables

  • Drone

System Overview

A Ground Control Station (GCS) in the form of a Linux laptop receives this positional data by listening to the broadcast from Vicon’s Host PC, reformats the positional data into MAVlink’s GPS_INPUT format, and sends it wirelessly over a Wi-Fi module to a flight controller.

GCS Setup

Download the following on the GCS laptop:

  • Vicon DataStream SDK 1.10.0 - Select Tracker. (Vicon)

  • pyvicon — a Python3 wrapper by MathGaron (GitHub)

Set Up a Conda Virtual Environment (Optional)

conda create -n VICON python=3.10
conda activate VICON

Pyvicon installation

Within the downloaded Vicon SDK, move shared library .so files into an accessible location for your OS (In my case, lib inside my “Vicon” venv). Move .cpp and .h files into pyvicon-master/pyvicon folder as well. Below is an example of how to do this:

# Move .so shared libraries into the venv lib folder
find ~/Downloads/ViconDataStreamSDK_1.10.0.123216h -name "*.so" \
    -exec mv {} ~/miniconda3/envs/VICON/lib/ \;

# Move .cpp source files into pyvicon
find ~/Downloads/ViconDataStreamSDK_1.10.0.123216h -name "*.cpp" \
    -exec mv {} ~/Downloads/pyvicon-master/pyvicon/ \;

# Move .h header files into pyvicon
find ~/Downloads/ViconDataStreamSDK_1.10.0.123216h -name "*.h" \
    -exec mv {} ~/Downloads/pyvicon-master/pyvicon/ \;

Install the following packages/dependencies:

sudo apt-get install libgtk-3-dev
sudo apt remove modemmanager -y
python3 -m pip install numpy==2.2.6
python3 -m pip install pathlib2==2.3.7.post1
python3 -m pip install matplotlib==3.10.9
python3 -m pip install opencv-python==4.13.0.92
python3 -m pip install Cython==3.2.4
python3 -m pip install future==1.0.0
python3 -m pip install wxpython==4.2.5

Note

wxpython can take up to 20 minutes to install. If the terminal appears to stall at that package, it is still working — do not interrupt the process.

From inside the pyvicon-master directory, build and install pyvicon:

cd ~/Downloads/pyvicon-master
python3 setup.py install

Network Setup

Find a means to connect the Vicon Host PC to your GCS laptop (I am using CAT6 ethernet for lowest latency) and rename its IP address as “vicon” in the hosts file. For example:

sudo nano /etc/hosts

# Example IP address
192.168.0.218 vicon

Press Ctrl+O and Enter to save, then Ctrl+X to exit.

Verify connectivity:

ping vicon

A flow of 64 bytes from vicon (192.168.0.218) messages confirms a successful connection between your GCS and the Vicon Tracker.

Drone Setup

Connect the Pixhawk6C to your computer and navigate to Config → Full Parameter List. Using the search box, set the following parameters:

Parameter

Value

AHRS_EKF_TYPE

3

EK3_SRC1_POSXY

3

EK3_SRC1_POSZ

3

EK3_SRC1_VELXY

3

EK3_SRC1_VELZ

3

EK3_SRC1_YAW

2

EK3_SRC2_POSXY (Same for SRC2’s VELXY, POSZ, VELZ, YAW)

0

EK3_SRC3_POSXY (Same for SRC3’s VELXY, POSZ, VELZ, YAW)

0

EK3_MAG_CAL

5

EK3_POSNE_M_NSE

0.002

GPS1_TYPE

14

GPS1_DELAY_MS

50

COMPASS_USE

0

COMPASS_USE2

0

COMPASS_USE3

0

These parameters configure the Extended Kalman Filter (EKF3) and GPS subsystem to accept Vicon data as the main position source and disable compass reliance.

Note

An empirical GPS1 delay of 50ms was found to work best with the Vicon system. If using a different network setup, you may need to adjust this value depending on your network latency.

For remote connection between GCS and the flight controller, I used an ESP8266 Wi-Fi module connected to a Pixhawk6C via the telemetry port. Update the SERIAL1_BAUD parameter to 921600 and SERIAL1_OPTIONS to 2 for this setup. If using a different telemetry module, you may need to adjust this value.

IR Marker Placement

Mount at least 4 IR markers on the drone using hot glue, positioning them where they are clearly visible from the camera’s perspective. Use an asymmetrical arrangement.

Note

If flying multiple drones simultaneously, each drone must have a geometrically distinct marker pattern to prevent the Vicon system from misidentifying objects.

Vicon Setup

Switch on the Vicon Positioning System and also the Vicon Host PC, allow the system to warm up (~20 minutes).

Creating a Camera Mask

Navigate to the CALIBRATE tab. Under CREATE CAMERA MASK, click START. This takes a snapshot of the environment and filters out any ambient IR reflections.

Calibrating the Cameras

Under CALIBRATE CAMERAS, click START. The computer will verbally confirm "Calibration started".

Prepare the Vicon Calibration Wand and switch on its LEDs. Enter the Vicon environment and sweep the wand in a cyclical arc facing the cameras, covering all camera positions in the arena. Camera calibration progress is indicated by LED colour change:

  • Small cameras: red/pink → green when calibrated

  • Large cameras: red → green, with an on-screen progress bar

Continue sweeping until all cameras turn from static green to static red, indicating complete calibration.

Return to the PC and check the CAMERA CALIBRATION FEEDBACK panel. Once the progress bar completes, inspect the World Error and Image Error values for all cameras.

Note

Any orange or red tiles in the table indicate a poor calibration — repeat the physical sweep in that case.

Emphasize your sweep in areas your drone is expected to fly. (e.g. if you are flying in the corner, do few more sweeps in that corner).

Setting the Origin

From within your Vicon environment, place the wand flat on the ground at your chosen origin location.

The direction convention for the Calibration Wand is usually known as: The bottom of the handle points towards West, the left handle points towards North. Align the wand as orthogonally as possible with your Vicon environment.

Warning

A poorly oriented origin will result in a skewed inertial coordinate frame, which will cause problems for any path-planning algorithms.

Leave the wand on the ground, return to the PC, and navigate to SET VOLUME ORIGIN. Click START. The computer will verbally confirm "Origin set".

Defining New Drone Objects

The Vicon system identifies objects by recognising the geometric arrangement of IR markers on a drone. To define a new object:

  1. Place the drone inside the Vicon environment.

  2. Align Autopilot’s forward direction with the origin’s North axis.

  3. On the PC, click the OBJECT tab.

  4. In the viewport (switch to 3D ORTHOGONAL to -Z if markers are not visible), use Alt+click to drag-select your IR markers. The selected markers will show which cameras are tracking them.

  5. At the bottom left of the screen, type a name for your object and click CREATE, then SHARED.

  6. Locate your newly created object in the object list and save it.

  7. Select your object in the list and ensure no other objects are selected.

Warning

Ensure your Autopilot’s North is aligned with Vicon’s North when declaring a new object, otherwise you will have a mismatch between body and inertial frame.

GCS integration

If you haven’t installed MAVProxy and pymavlink already:

python3 -m pip install pymavlink==2.4.49
python3 -m pip install mavproxy==1.8.74

You must tell MAVproxy which Vicon object to track. Navigate to the MAVProxy’s module folder and find mavproxy_vicon.py, for example:

~/miniconda3/envs/VICON/lib/python3.10/site-packages/MAVProxy/

Open mavproxy_vicon.py and edit lines 29–36:

  • Set origin_lat, origin_lon, and origin_alt to 0.

  • Set object_name to the name of your drone object as defined in the Vicon Tracker (e.g. [TroglodytesDrone]).

Save the file.

Ensure:

  • The GCS is connected to the Vicon Host PC.

  • The GCS is connected to the flight controller via Wi-Fi module/your means.

  • The drone is placed inside the Vicon environment and tracked by the Vicon system.

Launch MAVProxy:

mavproxy.py --master :<port_number> --console --map

Within the MAVProxy prompt, load and start the Vicon module:

module load vicon
vicon set
vicon start

A successful connection will print:

Connected to subject "<OBJECT_NAME>" segment "<OBJECT_NAME>"

The MAVProxy console should now display live position and Euler angles in North-East-Down and Roll-Pitch-Yaw coordinate system.

Warning

Vicon utilizes the NEU (North-East-Up) coordinate system, while ArduPilot uses NED (North-East-Down) coordinate system. Pyvicon automatically converts the coordinates from NEU to NED, but for your own custom integration, you must ensure this conversion is handled correctly (To fly 1m high in MAVlink format, this is -1, not 1).

Note

If the console reports a height of approximately -12cm while the drone is on the ground, this is expected — it reflects the offset between the drone’s base and the geometric centre of the IR marker cluster.

Checking Orientation

Monitor the Vicon status output in the MAVProxy console, carefully verify these values are consistent and sensible as you physically rotate and translate the drone before proceeding to flight.

Test Flight

Set the following flight mode assignments (using a 3-way switch on channel 5 or your preferred channel):

  • Flight Mode 1: Stabilize

  • Flight Mode 4: Alt Hold

  • Flight Mode 6: Loiter

Once the EKF3 reports yaw alignment and GPS lock, the drone is ready to arm. For the first flight, you should take off using Stabilize mode under your manual control. Once the drone is airborne and steady, attempt Alt Hold mode while being fully prepared to switch it back if something goes wrong. Once the drone is stable in Alt Hold using the Vicon coordinates, you can attempt Loiter mode and Guided mode.

Warning

Exercise great caution when attempting to fly in Alt Hold, Loiter mode for the 1st time. Visually imagine the drone’s ability to full throttle into the ceiling or suddenly drops out of the sky as the worst case scenario due to a misconfiguration. The moment you switch the modes you must be capable of switching back to Stabilize mode immediately if the drone is not behaving as expected.

Cranfield’s Indoor Flight Arena’s Approach

It’s because configuration differs between the lab environments, this serves as more of a working principle of Vicon integration with Ardupilot. For a more extensive “Dummy” Guide with specific hardware configurations we use in the Cranfield indoor flight arena, it is publicly available at: Vicon Indoor Positioning System with Pixhawk6C. Please use this as a reference for your own setup.

Warning

The ESP8266 is reported to have connection issues in swarm flights. Use a Raspberry Pi Wi-Fi hosting feature for remote communication if conducting multi-drone operations.

Not all Pixhawk variants behave identically with this configuration — older Radiolink Pixhawk hardware does not work.

This guide has not been tested with PX4 firmware.

Do not use Windows Subsystem for Linux (WSL) for the GCS — port communication permissions are difficult to configure correctly.