Open Source DIY Motion Capture

About

Pyxy3D (pixie-3D) is intended to serve as the core software component of a low-cost DIY motion capture studio. It is a python package that integrates:

multicamera calibration
2D (x,y) landmark tracking
3D landmark triangulation.

It is GUI-based and open-sourced under the LGPLv3.

Landmark tracking is based on a Tracker abstract base class. Variations of Google's Mediapipe have been implemented to illustrate use of this base class and how these calculations will flow automatically through the processing pipeline. Implementing alternate tracking tools (such as MMPose and DeepLabCut) is on the development roadmap.

Please see our docs for details about installation, project setup, and general workflow.

Demo Output

ballet_demo.mp4

The above was created using Pyxy3D, a 7 year old t440p laptop, and 4 webcams (~$25 each). This includes camera calibration, recording of synchronized frames (720p @ 24 fps), landmark detection, and point triangulation. Note that the webcam recording functionality is not in the current version, though will be restored in the future. Animated rig creation was done using an early stage Blender add-on project called Rigmarole

Quick Start

Please note that given the size of some core dependencies (OpenCV, Mediapipe, and PySide6 are among them) installation and initial launch can take a while.

Basic Installation and Launch

Windows

# Open Command Prompt and navigate to directory that will hold venv
# this does not need to be the same as where your project workspace is held
cd path\to\your\project

# Create a virtual environment named 'env' using Python 3.10
"C:\Path\To\Python3.10\python.exe" -m venv .venv

# Activate the virtual environment
.\env\Scripts\activate

# Your virtual environment is now active.
# You can install using pip
pip install pyxy3d

# Launch from the command line
pyxy3d

MacOS/Linux

# Open Command Prompt and navigate to directory that will hold venv
# this does not need to be the same as where your project workspace is held
cd path/to/your/project

# Create a virtual environment named 'venv' using Python 3.10
/path/to/python3.10 -m venv .venv

# Activate the virtual environment
source .venv/bin/activate

# Your virtual environment is now active.
# You can install using pip
pip3 install pyxy3d

# Launch from the command line
pyxy3d

Basic Steps

Once the GUI launches, navigate to File->New/Open Project and create a folder to hold your project

A basic project structure will be created here

Define a Charuco calibration board via the Charuco tab and print it out, fixing it to something flat
Record footage for the calibration according to the guidelines for the intrinsic and extrinsic calibrations.
Record synchronized motion capture trials
Store video files within the project folder and reload the workspace
Run autocalibration on all cameras within the Cameras tab
Run "Calibration Capture Volume" from the Workspace Tab
Set origin within the capture volume (optional but helpful)
Run post-processing on individual recordings to generate 3D trajectory output

Key Features

Calibration board creation

Easy creation of png files for ChArUco calibration boards
board definition can be changed across intrinsic and extrinsic calibration allowing greater flexibiltiy

Intrinsic Camera Calibration

Automated calculation of camera intrinsic properties from input video
- Optical Center
- Focal Length
- Lens Distortion
Visualization of distortion model to ensure reasonableness

Extrinsic Camera Calibration

Automated bundle adjustment to estimate 6 DoF relative position of cameras
Visualizer to inspect the estimates from the bundle adjustment
Setting of the World Origin within the visualizer to simplify data processing

3D Tracking

Tracker API for integrating alternate tracking methods
- 3 sample implementations with Google Mediapipe (Hands/Pose/Holistic)
Automated application of landmark tracking to synchronized videos
Triangulation of 3D landmark position based on calibrated cameras
Gap-filling and butterworth filtering to smooth trajectory estimates

Trajectory Output

output to .trc file format for use in biomechanical modelling
output to tidy .csv format with well-labelled headers for straightforward integration with other workflows
companion project Rigmarole in development to facilitate creation of animated rigs in Blender

Limitations

Requires Frame Sync

The workflow currently requires you to provide your own synchronized frames or to provide a file that specifies the time at which each frame was read so that pyxy3d can perform the synchronization itself. There are plans to manage this synchronization automatically through audio files, though that has not yet been implemented.

Currently only using Mediapipe

Google's Mediapipe provides a relatively easy and efficient method for human subject tracking, though for many uses it is limiting. Pyxy3D has a general Tracker base class that is implemented in a few versions (Pose/Hands/Holistic). This has provided a proof of concept implementation of markerless tracking, though for more robust use the roadmap calls for integration with more powerful tools such as MMPose and DeepLabCut.

Reporting Issues and Requesting Features

To report a bug or request a feature, please open an issue. Please keep in mind that this is an open-source project supported by volunteer effort, so your patience is appreciated.

General Questions and Conversation

Post any questions in the Discussions section of the repo.

Acknowledgments

This project was inspired by FreeMoCap (FMC), which is spearheaded by Jon Matthis, PhD of the HuMoN Research Lab. The FMC calibration and triangulation system is built upon Anipose, created by Lili Karushchek, PhD. Pyxy3D was originally envisioned as an alternative calibration tool to Anipose that would allow more granular estimation of intrinsics as well as visual feedback during the calibration process. Several lines of of the original Anipose triangulation code are used in this code base, though otherwise it was written from the ground up. I'm grateful to Dr. Matthis for his time developing FreeMoCap, discussing it with me, pointing out important code considerations, and providing a great deal of information regarding open-source project management.

License

Pyxy3D is licensed under LGPL-3.0. The triangulation function was adapted from the Anipose code base which is licensed under BSD-2 Clause.

mprib/pyxy3d