Comparison of the marginal median (left) to the spatial median, or LAD estimation (right). Plotted are the estimation biases Δe for 10⁶ simulation runs, shown as a density in grayscale. Over-plotted are arbitrary contours of increasing density (equal in both plots), to highlight the anisotropy in P(Δe). Since e₁ and e₂ depend on the choice of reference frame, the marginal median introduces an artificial anisotropy. For the LAD estimations, the residual distances | r_i | do not depend on the choice of reference frame.