Comparison of different camera calibration approaches for underwater applications

Abstract

a b s t r a c tThe purpose of this study was to compare three camera calibration approaches applied to underwater applications: (1) static control points with nonlinear DLT; (2) moving wand with nonlinear camera model and bundle adjustment; (3) moving plate with nonlinear camera model. The DVideo kinematic analysis system was used for underwater data acquisition. The system consisted of two gen-locked Basler cameras working at 100 Hz, with wide angle lenses that were enclosed in housings. The accuracy of the methods was compared in a dynamic rigid bar test (acquisition volume-4.5 Â 1 Â 1.5 m 3 ). The mean absolute errors were 6.19 mm for the nonlinear DLT, 1.16 mm for the wand calibration, 1.20 mm for the 2D plate calibration using 8 control points and 0.73 mm for the 2D plane calibration using 16 control points. The results of the wand and 2D plate camera calibration methods were less associated to the rigid body position in the working volume and provided better accuracy than the nonlinear DLT. Wand and 2D plate camera calibration methods presented similar and highly accurate results, being alternatives for underwater 3D motion analysis.

Normative 3D opto-electronic stereo-photogrammetric posture and spine morphology data in young healthy adult population

“…Therefore, the computerised calibration of the internal and external parameters is enabled simply by surveying and capturing the 3D movement of a rigid bar (wand) with three markers at a known distance, in motion inside the working volume. This approach overcomes working volume limits of previously proposed methods such as Direct Linear Transformation (DLT) [63] and provides far better results [64]; see also Chiari et al [65] for review. The final mean 3D stereo-photogrammetric error was limited to a range of 0.3–0.4mm throughout the entire working volume.…”

Assessment of three-dimensional joint kinematics of the upper limb during simulated swimming using wearable inertial-magnetic measurement units

“…The limits of using simulated swimming may be identified as follows: (1) the swimmer is positioned with the legs constrained; (2) the range of motion of body roll is smaller; (3) there is no buoyancy, forcing the participant to hold the trunk using the lumbar muscles; (4) there is no water resistance on the hands; and (5) there is no drag effect at all. However, the choice of using simulated swimming was motivated by a number of reasons: (1) the gold standard is more accurate than conventional underwater video-camera systems (Magalhaes et al, 2013;Silvatti, Dias, Cerveri, and Barros, 2012;Silvatti et al, 2013), (2) the whole swimming stroke cycle can be recorded, more than one stroke cycle can be analysed, and (3) all the procedures can be better controlled. Moreover, the differences between simulated and real swimming can be considered negligible for the validation of the 3D joint kinematic in a reliable context.…”

3d Documentation of Archeological Remains in the Underwater Park of Baiae

“…Optical techniques give better performances in presence of clear water and in close range applications. Among the optical techniques, photogrammetry has known a notable development during the last decade (Bruno et al, 2011;Silvatti et al, 2012), with a particular attention for the dense stereo mapping technique (Lowe, 2004). The latter, compared to the active ones, allows for a fast and accurate 3D survey through standard photographic equipment (Bianco et al 2013).…”