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Abstract
This article describes a method that allows estimating, with the 2D version of the direct linear transformation (DLT), the actual 2D coordinates of a point when the latter is not strictly in the calibration plane. Markers placed in vertical line, above, below and in the centre of a horizontal calibration plane were filmed by a moving camera. Without correction, strong errors (up to 64.5%) were noticed for markers out of the calibration plane. After correction, calculated coordinates were consistent with actual values (error < 0.55%). The method was then applied to slip distance measurement, using a marker fixed on the hoof of a horse trotting on a calibrated track while being followed with a camera. The correction effect represented 6.6% of slip distance. Combined with the 2D-DLT transformation, the proposed corrective method allows an accurate measurement of slip distances, for high-speed outdoor locomotion analysis, using a moving camera.
Acknowledgements
The authors would like to thank the Conseil Régional de Basse-Normandie, the Fonds unique interministériel, The French Ministry of Agriculture, the Institut Français du Cheval et de l'Equitation and the FEDER for their financial support to this project, and the Pôle de compétitivité Filière Equine for their technical assistance.
Conflict of interest statement: The authors have no conflict of interest to disclose.