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Graphical explanation of the function ψ (κ). (a) shows the relationship between κ and a using a red curve with radius of curvature r. (b) Curves in red color show the case for evenly spaced κ. Curves in green show when α = ψ (κ) is evenly spaced. Notice that green curves exactly intersect at corresponding angles whereas red ones are close but do not exactly match the angles.
