Fig 3. The calculation of the similarity measure BLD.

First, the minimum “forward” distance $d_{\text{min}}(p,{\mathcal{E}}_{j^{\prime }}^s)$ between the point $p\in {\mathcal{E}}_j^s$ and the contour ${\mathcal{E}}_{j^{\prime }}^s$ is determined, here marked as (1). Second, among all the points q on ${\mathcal{E}}_{j^{\prime }}^s$ with a “inverse” minimum distance $d_{\text{min}}^{-1}(q,{\mathcal{E}}_j^s)$, those are selected whose minimal distance is found at the point p. Here, q and $\tilde{q}$ are the candidates, with the corresponding distances denoted by (2) and (3). Then, the maximum distance among the candidates, in this case (2), is chosen as $d_{\text{max}}^{-1}({\mathcal{E}}_{j^{\prime }}^s,p)$. Finally, $\text{BLD}(p,{\mathcal{E}}_{j^{\prime }}^s)$ is defined as the maximum between $d_{\text{min}}(p,{\mathcal{E}}_{j^{\prime }}^s)$ and $d_{\text{max}}^{-1}({\mathcal{E}}_{j^{\prime }}^s,p)$, in this example (2). For more details see [30].