Compute the Blomqvist's Beta $\beta_\mathbf{C}$ of a copula (Nelson, 2006, p. 182), which is defined at the middle of $\mathcal{I}^2$ as$$\beta_\mathbf{C} = 4\times\mathbf{C}\biggl(\frac{1}{2},\frac{1}{2}\biggr) - 1\mbox{,}$$
where the $u = v = 1/2$ and thus shows that $\beta_\mathbf{C}$ is based on the median joint probability. Nelson also reports that although, Blomqvist's Beta depends only on the copula only through its value at the center of $[0,1]\times[0,1]$, it nevertheless often provides an accurate approximation to Spearman's Rho rhoCOP and Kendall's Tau tauCOP.