Visualisation of the different influence functions before (φ₀ left side of the panels) and after (ψ_⊥, right side of the panels) orthogonalisation for the different profiles. The 2D maps are normalised to their maximal value. Panel a: 2D local piston. Panel b: 2D pyramid. Panel c: 2D axisymmetric Gaussian profile. Panel d: 2D axisymmetric ALPAO profile. Panel e: 2D sine function. Panel ſ: x₁ -profiles of the different influence functions before (solid lines) and after (dashed lines) orthogonalisation.