632195.fig.004a
(a)
632195.fig.004b
(b)
Figure 4: Estimating distances from a set of surface points to an estimated surface in (a) the original coordinate system, the error estimated by the observable variable (dashed lines) differs greatly from the actual error (solid lines), but if (b) the pleural surface is parallel to the explanatory variable plane, the error estimated by the observable variable provides a good approximation to the actual error.