Fig 2. Skull variants along the two principal components with the largest eigenvalues.

We visualize $\overline{\mathbf{s}}+{\alpha }_1{\mathbf{u}}_1+{\alpha }_2{\mathbf{u}}_2$, where α_i = a_i ⋅ σ_i, i = 1, 2, is the weight containing the standard deviation σ_i to the corresponding eigenvector u_i, and the factor a_i ∈ {−2, 0, 2}.