In the context of layered sketches, where the view depth of stroke points are computed independent of its neighbouring points, we find curve smoothness to be an important fitness criterion. Considering curves are segmented by points of high curvature we expect resulting curves to be reasonably smooth. Therefore, if the max variation in the view depth of the generated curve is greater than ν (default ν is 0.4) the curve is deemed not smooth. As surface normals aligned with the view direction can result in highly foreshortened normal plane curve projections,low foreshortening is another fitness criterion. If v min/v max (min over max view depth of the curve) is lower than µ (default µ is 0.5), the curve is considered overly foreshortened. In practice this happens rarely, but in the case of these classified 3D curves of poor quality or No-Type curves shown in the user study of Section 5, we replace the interpreted curve by the fittest minimum skew viewplane or X Y Z planar curve. In other words, if just one of the curve end-points is defined in 3D we project the stroke onto the least foresfhortened of three planes aligned with the XY Z axes and passing through the 3D end-point. If both end-points are known in 3D we project the stroke onto the minimum-skew viewplane passing through the two 3D end-points. These alternate planar curve interpretations can also be forced by a user holding the space key.