title: Error analysis of a direct current electromagnetic tracking system in digitizing 3-dimensional surface geometries.
abstract: The direct current electromagnetic tracking device has seen increasing use in biomechanics studies of joint kinematics and anatomical surface geometry. In these applications, a stylus is attached to a sensor to measure the spatial location of three-dimensional landmarks. Stylus calibration is performed by rotating the stylus about a fixed point in space and using regression analysis to determine the tip offset vector. Measurement errors can be induced via several pathways, including; intrinsic system errors in sensor position or angle and tip offset calibration errors. A detailed study was performed to determine the errors introduced in digitizing small surfaces with different stylus lengths (35, 55, and 65 mm) and approach angles (30 and 45 degrees) using a plastic calibration board and hemispherical models. Two-point discrimination errors increased to an average of 1.93 mm for a 254 mm step size. Rotation about a single point produced mean errors of 0.44 to 1.18 mm. Statistically significant differences in error were observed with increasing approach angles (p < 0.001). Errors of less than 6% were observed in determining the curvature of a 19 mm hemisphere. This study demonstrates that the "Flock of Birds" can be used as a digitizing tool with accuracy better than 0.76% over 254 mm step sizes.
authors.affiliation: Department of Surgery and School of Biomedical Engineering, Dalhousie University, 5981 University Avenue, Halifax, NS, Canada, B3H 3J5.
authors.forename: A D
authors.initials: AD
authors.lastname: Milne
authors.forename: J M
authors.initials: JM
authors.lastname: Lee
mesh_terms: D001696:Biomechanical Phenomena; D003198:Computer Simulation; D055590:Electromagnetic Phenomena / Q000295:instrumentation*; D021621:Imaging, Three-Dimensional; D012984:Software