Illustration of the process of tracing a real arc in its image. The left panel shows the five p points used to compute the arc length. The right panel shows the high-intensity m points (dashed circles) used to find p_max for the same arc. The center and radius of curvature are determined as the circle containing the points p₁,p₂, and p_max = m₂. The width is based on the line through the central point p₃, whereas the asymmetric major-axes a₁ and a₂ are the lengths of the segments connecting m₂ = p_max to the arc extremes p₁ and p₂.