9.5.2

232 • CHAPTER 7
OBJECTS MENU • NURBS • 233
Banking enabled (left) and disabled (right).
Banking allows you to use arbitrary 3D paths. However, it is not suitable for a precise sweep since the
contours may break up, depending on the path.
If the Banking option is disabled, the following applies: the contour spline is rotated for each
subdivision so that on the one hand its Z-axis is always tangential to the path spline and on the other
hand its X-axis is parallel to the XZ plane of the path spline. You can use this XZ plane to control the
sweep, although you do lose the ability to model loops, since the contour ips over when the path
runs vertically.
Finally, there is another, much more powerful functionality — you can use a rail spline to control the
direction and/or scale of the contour as it runs along the path. The path spline controls the positioning
of the subdivisions. Adaptive spline interpolation is usually a good choice since it generates a relatively
low number of surfaces. Uniform spline interpolation, on the other hand, is the better choice for
animation since the subdivisions will be a uniform distance apart.
A common mistake when using rail splines is to use a path spline with adaptive interpolation. This can
generate insufcient subdivision for the rail to work properly — a higher resolution is required. You
can solve the problem by setting the path’s Intermediate Points to Natural.
Intermediate Points set to Adaptive (left) and Natural (right).