Calibration of multiple cameras for large-scale experiments using a freely moving calibration target
K. Muller (TU Delft - Fluid Mechanics)
C.K. Hemelrijk (Rijksuniversiteit Groningen)
J Westerweel (TU Delft - Fluid Mechanics)
Daniel S.W. See-Wai Tam (TU Delft - Fluid Mechanics)
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Abstract
Abstract: Obtaining accurate experimental data from Lagrangian tracking and tomographic velocimetry requires an accurate camera calibration consistent over multiple views. Established calibration procedures are often challenging to implement when the length scale of the measurement volume exceeds that of a typical laboratory experiment. Here, we combine tools developed in computer vision and non-linear camera mappings used in experimental fluid mechanics, to successfully calibrate a four-camera setup that is imaging inside a large tank of dimensions ∼10×25×6m3. The calibration procedure uses a planar checkerboard that is arbitrarily positioned at unknown locations and orientations. The method can be applied to any number of cameras. The parameters of the calibration yields direct estimates of the positions and orientations of the four cameras as well as the focal lengths of the lenses. These parameters are used to assess the quality of the calibration. The calibration allows us to perform accurate and consistent linear ray-tracing, which we use to triangulate and track fish inside the large tank. An open-source implementation of the calibration in Matlab is available. Graphic abstract: [Figure not available: see fulltext.].
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