eWand: A calibration framework for wide baseline frame-based and event-based camera systems
Thomas Gossard, Andreas Ziegler, Levin Kolmar, Jonas Tebbe, Andreas Zell
TL;DR
eWand tackles the challenge of extrinsic calibration for multi-camera systems with wide baselines by enabling joint frame- and event-based calibration using blinking LEDs inside opaque spheres. The method replaces 2D targets with a wand-based marker system and uses a bundle adjustment framework to optimize extrinsics, with intrinsic calibration kept separate. Experiments with four frame-based and two event-based cameras show reprojection errors comparable to Kalibr and 3D positional errors close to state-of-the-art, while offering easier handling and faster setup. This work enables practical, scalable calibration of hybrid camera setups for robotics and perception tasks.
Abstract
Accurate calibration is crucial for using multiple cameras to triangulate the position of objects precisely. However, it is also a time-consuming process that needs to be repeated for every displacement of the cameras. The standard approach is to use a printed pattern with known geometry to estimate the intrinsic and extrinsic parameters of the cameras. The same idea can be applied to event-based cameras, though it requires extra work. By using frame reconstruction from events, a printed pattern can be detected. A blinking pattern can also be displayed on a screen. Then, the pattern can be directly detected from the events. Such calibration methods can provide accurate intrinsic calibration for both frame- and event-based cameras. However, using 2D patterns has several limitations for multi-camera extrinsic calibration, with cameras possessing highly different points of view and a wide baseline. The 2D pattern can only be detected from one direction and needs to be of significant size to compensate for its distance to the camera. This makes the extrinsic calibration time-consuming and cumbersome. To overcome these limitations, we propose eWand, a new method that uses blinking LEDs inside opaque spheres instead of a printed or displayed pattern. Our method provides a faster, easier-to-use extrinsic calibration approach that maintains high accuracy for both event- and frame-based cameras.