Consider any X,Y ∈ ∂I. Choose X and Y such that d(X,Y ) = D(I). Find Z,W ∈ ∂I maximizing D⊥ = d(Z,W) on the set of all pairs of ∂I that define a segment orthogonal to [XY]. The aspect ratio is defined as the quotient D(I)/D⊥. Values close to 0 indicate an elongated shape.