The merging routine repeatedly merges adjacent segments. For every i^th segment, the program attempts to merge it with i – 1^st and i + 1^st. Let these new segments be seg₁ and seg₂. The fit error for them is calculated. For the segment with least error among seg₁ and seg₂, merging happens only if the error is less than the sum of the corresponding errors of the original segments. The image shows the program merging lines L₄ and L₅ into arc A₄. It also merges arcs A₁, A₂, and A₃ into one arc, A₅.