VICAN: Very Efficient Calibration Algorithm for Large Camera Networks

VICAN uses a primal-dual bipartite PGO solver to 1) calibrate an object 2) estimate poses of a camera network. See the extended paper for details. A Jupyter notebook is provided in main.ipynb exemplifying the usage of VICAN. A shorter tutorial on colab is available!

Cite as:

Gabriel Moreira, Manuel Marques, João Paulo Costeira, Alexander Hauptmann, VICAN: Very Efficient Calibration Algorithm for Large Camera Networks, IEEE International Conference on Robotics and Automation (ICRA), 2024.

Dataset

Dataset is provided here.

• No images - preferred The fastest way of using the dataset is by downloading only the already computed camera-marker pairwise pose dictionaries small_room/cam_marker_edges.pt, large_shop/cam_marker_edges.pt, cube_calib/cam_marker_edges.pt. For each scene, you will also find the ground-truth camera data in small_room/cameras.json, large_shop/cameras.json with (t, R, fx, fy, cx, cy, distortion, resolution_x, resolution_y). See Colab Notebook for an example.
• Using the images Instead, you may download cube_calib.tar.xy, large_shop.tar.xy and small_room.tar.xy. These contain all the images necessary to reproduce the pose estimation results. The structure of the folders is <dataset>/<timestep>/<camera_id>.jpg. For example small_room/0/1.jpg is an image captured by camera "1" at time 0. The ground-truth camera data dictionary is already included in each .tar.
• Using 3D models You can also download the 3D model Blender files large_shop.blend and small_room.blend and run the rendering script yourself. Beware that this takes several hours. The dataset can be rendered by calling the Python provided with the Blender installation blender -b <path to Blender file> --python render.py (Blender 3.0.0). Edit render.py according to the number of ray-tracing samples (default: 100), number of timesteps (5k for small_room, 10k for large_shop). Blender camera data will be stored as a dictionary in <dataset name>_render/cameras.json, at the beginning of the render. Cube pose per timestep will be stored in dictionaries <dataset name>object_pose_<n>.json. The n just specifies the number of the core that created that file.

Reproducing the results

Clone the repository and download the data. Set up the files as:

• vican/
• render.py
• main.ipynb
• small_room/
  • cameras.json
  • cam_marker_edges.pt
  • 0/
    • 1.jpg
    • 2.jpg
    • ...
  • ...
• large_shop/
  • cameras.json
  • cam_marker_edges.pt
  • 0/
    • 182.jpg
    • 184.jpg
    • ...
  • ...
• cube_calib/
  • cam_marker_edges.pt
  • 0/
    • 0.jpg
  • ...

1. Object calibration

The setup is a static camera and an object moving in its field-of-view. Images should be stored as <object_root>/<timestep>/<timestep>.jpg. Camera dictionary should be stored in <object_root>/cameras.json. Initialize a Dataset instance and call estimate_pose_mp in order to detect markers and compute camera-marker poses (via OpenCV arUco corner detection + PnP, in parallel). Note that you can avoid this step by downloading cube_calib/cam_marker_edges.pt directly. From here, to optimize the object marker poses call object_bipartite_se3sync. The arguments are similar to those used for camera calibration with a different naming convention i.e., the src_edges keys are of the form (timestep, timestep_markerid), where the marker id is the arUco marker ID. The output of object_bipartite_se3sync is a dictionary with keys being the object marker IDs and values being the SE3 pose of each marker in the world frame (as if the object was static and the camera was moving around it).

2. Camera pose estimation

The setup is a large scene covered by static cameras and an object moving in the field-of-view of a subset of them. Images should be stored as <dataset_root>/<timestep>/<camera_id>.jpg. Cameras dictionary should be stored in <dataset_root>/cameras.json. Initialize a Dataset instance and call estimate_pose_mp in order to detect markers and compute camera-marker poses (via OpenCV arUco corner detection + PnP, in parallel). Note that you can avoid this step by downloading large_shop/cam_marker_edges.pt or small_room/cam_marker_edges.pt directly. To optimize the set of camera poses given these camera-object edges, call bipartite_se3sync. The arguments are

• src_edges: a dictionary with keys (camera id, timestep_markerid), for example the edge ("4", "10_0") corresponds to the pose of marker with ID "0" detected at time t=0, in the reference frame of camera with ID "4". The values of the dataset are a dictionary containing "pose" : SE3, "reprojected_err" : float, "corners" : np.ndarray, "im_filename" : str.
• noise_model_r: Callable (float) that estimates concentration of Langevin noise given the edge dictionary;
• noise_model_t: Callable (float) that estimates precision of Gaussian noise from given the edge dictionary;
• edge_filter: functional (bool) that discards edges based on the edge dictionary;
• maxiter: maximum primal-dual iterations;
• lsqr_solver: "conjugate_gradient" or "direct". Use the former for large graphs. The output of bipartite_se3sync is a dictionary with the camera IDs as keys and values being the SE3 pose of each camera in the world frame.

Pipeline for camera network calibration using arUco markers:

You may use the same pipeline for other datasets of static cameras + moving objects covered with markers. Just make sure to use the same format for the camera pose estimation folder: <dataset>/<timestep>/<camera_id>.jpg and have camera data stored in <dataset_root>/cameras.json. For object calibration your folder should follow the format <object_root>/<timestep>/<timestep>.jpg. Then:

• Object pose estimation: object_dataset=Dataset(root=<object_root>) -> edges=estimate_pose_mp(object_dataset,...) -> object_edges = object_bipartite_se3sync(src_edges=edges,...)
• Camera pose estimation: dataset=Dataset(root=<dataset_root>) -> edges=estimate_pose_mp(dataset,...) -> bipartite_se3sync(src_edges=edges, constraints=object_edges,...) The output is a dictionary with poses w.r.t. world frame.

General camera network calibration

The optimization step is applicable to any setup consisting of a moving object and static cameras. Provided you have object poses relative to a subset of the cameras at each timestep in the same format as above, and provided you know the relative transformations between faces/nodes of the object, then you can simply use bipartite_se3sync(src_edges=edges, constraints=object_edges,...) to optimize for the camera poses.

See main.ipynb for a tutorial.

March, 2024