Error analysis of a direct current electromagnetic tracking system in digitizing 3-dimensional surface geometries.

Area of Science:

• Biomechanics
• Biomedical Engineering
• Motion Analysis

Background:

• Direct current electromagnetic tracking devices are increasingly utilized in biomechanics.
• These systems measure joint kinematics and anatomical surface geometry using a stylus sensor.
• Accurate spatial location of 3D landmarks is crucial for these applications.

Purpose of the Study:

• To investigate measurement errors in electromagnetic tracking systems.
• To evaluate the impact of stylus length and approach angle on digitization accuracy.
• To determine the reliability of the "Flock of Birds" system for digitizing small surfaces.

Main Methods:

• Stylus calibration using regression analysis to determine tip offset.
• Digitization of small surfaces using varying stylus lengths (35, 55, 65 mm) and approach angles (30, 45 degrees).
• Utilized a plastic calibration board and hemispherical models for error assessment.

Main Results:

• Two-point discrimination errors averaged 1.93 mm for a 254 mm step size.
• Rotation about a single point yielded mean errors between 0.44 and 1.18 mm.
• Increasing approach angles significantly increased errors (p < 0.001); curvature determination errors were under 6% for a 19 mm hemisphere.

Conclusions:

• Electromagnetic tracking systems are susceptible to errors from sensor inaccuracies and calibration issues.
• Stylus length and approach angle significantly influence digitization precision.
• The "Flock of Birds" system can function as a digitizing tool with accuracy better than 0.76% over 254 mm step sizes.