Sweep object

The sweep object (comparable to a path object or hose object) requires one to three splines. The first spline (contour spline) determines the cross-section of the hose cover, the second determines the path along which the first spline is to be moved. An additional path spline can also be used - this is then called a railspline. Instead of a railspline, you can also use the easier-to-use function graphs described below, which provide the most important functions of a railspline.

In the following scene, all objects were created from sweep objects (except for the ribbon cable path spline, the scene is completely parametric).

The contour spline is always arranged along its Z-axis on the path spline. If you have a two-dimensional path spline, you do not need to worry about the arrangement. With a three-dimensional path, however, things are a little more complicated:

If the Banking option is activated, the following rules apply: the contour spline is rotated at the starting point of the path spline so that its X-axis is parallel to the middle plane of the path spline. As before, its Z-axis is arranged tangentially to the path spline. All further contours are now determined in such a way that the angles change only minimally compared to the last contour. To ensure that the start and end contours of closed path splines always match exactly, a rotation is added to the contour if necessary to make this possible.

Banking allows you to use completely free 3D paths, but is less suitable for precise arrangements, as the contours can rotate unexpectedly depending on the path.

If the Banking option is not activated, the following applies: the contour spline is always rotated for each subdivision so that its Z-axis is tangential to the path spline and its X-axis is parallel to the XZ plane of the path spline. By defining this XZ plane, you can precisely control the arrangement behavior, but lose the option of modeling Loops, as the contour twists on the vertical rise.

Finally, you have a much more powerful option: you can always use a railspline that precisely controls the direction and/or size of each individual point.

The path spline specifies the points at which a subdivision is created. The adaptive subdivision is very well suited for modeling, as few areas are created, while the uniform subdivision is particularly suitable for animation, as the subdivisions do not jump to a new arrangement.

Problems with tilting contour splines

One of the most common problems with the sweep object is the seemingly unmotivated tilting of the contour spline when moving along the path spline. As is so often the case, the reason lies in complex mathematics, which we do not want to burden you with. To solve the problem, look at the following illustration:

In Figure 1. you will recognize the highlighted problem: The contour spline suddenly changes orientation. For Figure 2. Banking has been activated, but this only partially solves the problem, as the contour is twisted. The two solutions can be found in 3. and 4. In 3. the X/Y dimension of the contour was swapped and Banking was activated. At 4. you can also manage without Banking, but you have to define a rail spine.