Decision graphs for the artificial Lamb–Oseen vortex flow of Fig. 5 based on the ρ − δ thresholds of Eq. (22), (top) and on the γ threshold of Eq. (23), (bottom). In the bottom panel, n represents the datapoint number in increasing order of γ. Dotted lines represent the ρ and δ thresholds, while dashed lines show the γ threshold. Each point corresponds to a EVC. The green and pink starred EVCs satisfy both thresholds and are therefore selected as cluster centers.