When working with Edit Curves, it is important to understand the implications of working with the U location parameter. When altering the U value of a control point, the physical location of the point is not changing; rather it is the alignment to adjacent cross-section U locations. For example, take two adjacent circular cross-sections, one of which is an Edit Curve. If the bottom control point of the Edit Curve is changed from U = 0.25 to U = 0.5, then the feature line passing through the bottom of the Edit Curve will now pass through the left side of the adjacent circle. All of the interpolated segments between U = 0.5 and the remaining control points will be “squished” until the curve is reparametrized by arc length. Another parameter that affects the U locations along a curve is the Spin parameter, which effectively alters the U origin point. By combining Edit Curve U locations and Spin, the user has significant control over how feature lines and interpolated segments pass between adjacent cross-sections.
Another important feature of Edit Curves is the ability to enforce G1 continuity or slope continuity through a Bezier control point. Activating the G1 button for a control point will enforce the adjacent tangency points to pass through at the same angle similar to setting angles equal in Skinning. However, the strengths or lengths of those tangency vectors need not be equal e.g., equal curvature is not enforced. Applying G1 continuity is a great way of ensuring that your Edit Curves pass smoothly through a control point.