Abstract：A constrained implicit equation is developed to enhance the robustness and precision of perspective contour extraction for cylinders. The contour curve fitting problem is converted to a nonlinear optimization problem containing nonlinear constraints by a linear approximation. The problem is then solved with a rough estimate of the curve parameters and the noisy points filtered to find reasonable points based on the rough estimate of the curve parameters. This constrained problem is then converted to an unconstrained problem using the penalty function method to find the solution. This method takes advantage of the constraint between the lines and the ellipse to give better anti-noise performance for perspective cylinder contour extraction than separate methods using lines or ellipses. Tests of synthetic and real images show that this method effectively improves perspective contour curve fitting for cylinders.
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