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Extrinsic camera calibration for non-overlapping cameras with Gray code projection

Journal Contribution - Journal Article

Multi-camera setups require the transformations between the involved cameras to be known. The intrinsic camera calibration can be done relatively easily in advance in lab conditions before positioning the cameras. The extrinsic calibration on the other hand can only be obtained when the cameras are mounted in their final position. This is usually done using checkerboards or similar markers, which require some degree of overlap of the field of view. In this work, we propose a method where Gray code is projected on a plane (floor or wall) using a standard projector. The extrinsic calibration is found using a bundle adjustment method that optimizes the pose of the plane and the cameras with respect to the projector. No overlap is required in the field of view of the cameras; it is enough that in each camera part of the Gray code pattern is visible. A sensitivity analysis is performed on simulated images. The method has a low sensitivity to sensor noise and to errors in the intrinsic calibration of the projector. Using real-world experiments, we show that the method is accurate for both overlapping and non-overlapping cameras, with median rotation errors of 0.36 degrees and below. The accuracy of the proposed method is comparable to the state of the art, but this method provides a more practical procedure: no checkerboards must be held in place and only one projector pose is needed.
Journal: Optics and Lasers in Engineering
ISSN: 0143-8166
Volume: 134
Number of pages: 11
Publication year:2020