A method to minimise error in 2D-DLT reconstruction of non-planar markers filmed with a moving camera

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.

A Method-Comparison Study Highlighting the Disparity between Osseous- and Skin-Based Measures of Foot Mobility

“…Radiographic images were saved in DICOM format and postprocessed using Matlab software (MathWorks Inc., Natick, MA). After the application of a two-dimensional direct linear transformation to correct image distortion (22), the coordinates of the centroid of each radio-opaque skin marker were automatically identified and used to determine skin-based, noncontact radiographic measures of foot mobility. For skin-based radiographic measures of foot mobility, dorsal arch height was defined as the distance of the dorsal foot marker to the support surface, whereas midfoot width was defined as the distance between medial and lateral foot markers (1,4).…”