Cinema 4D / BodyPaint 3D Program Documentation Tutorials Mechanical Modeling Tutorial Modeling with Splines and Generator Objects
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Sweep Object

Objects such as piping, hoses, cables, or even paper clips or springs can be created using a uniform cross-section that follows a defined path. This is what the Sweep object does. As with the other Generator objects, Splines must also be made Child objects of the Sweep object. The order in which the Child objects lie in the hierarchy is important. The cross-section Spline must lie at the top of the hierarchy and below it the path Spline. The image below illustrates the proper order using a Spline used in conjunction with a Circle cross-section. This method lets you easily create wires, hoses, cables and similar objects. In the image below, a Freehand Spline was created in the front view and a scaled down Circle Spline Primitive was used as the cross-section.

Defining a Sweep object

The Sweep object object’s End Scale and End Rotation parameters let you modify the cross-section along the path. The Start Growth and End Growth parameters let you define in percent where the along the path the Sweep object object should begin and where it should end. Setting the Start Growth value to 50% and the End Growth value to 100% will result in the Sweep object object beginning at the path’s mid point and continuing to its end. Splines must be setup in the XY view, i.e., front viewport, before applying the Sweep object. Most of the Sweep object parameters are for modifying the orientation or scaling of the cross-section along the path. The Constant Cross Section option, for example, automatically scales the cross-section at locations where the path makes an abrupt change of direction, in order to maintain the cross-section’s integrity. The Rail options make it possible to calculate additional Spline curves that lie below the path Spline in the Sweep object hierarchy. This allows the cross-section to be scaled or rotated individually and any point along the path. However, this can be done even more comfortably using the parameters in the Details menu below.

Varying the profile

The Details menu contains two curves that can be used to adjust the cross-section’s Scale or rotation along the Spline. An example of what this can look like is shown in the image below. The length of the curve represents the length of the path. The curve’s amplitude (vertical position) defines the scaling along the path.

New points can be added by simply clicking on the curve. Points can be deleted by dragging them up out of the graph window. Click on the arrow to the left of each graph to make additional parameters available for that graph. These parameters can be used to define the exact position of a given point or the curve’s tension.

Modifying the cross-section rotation

The same principle is applied for rotating the cross-section along the path using the Rotation curve. In order to make this effect more apparent we substituted a Flower - Spline Primitive for the Circle Spline in the image below. The Rotation curve works just like the Scale curve with the exception that its zero point lies at the (horizontal) center of the curve. The From and To values define the rotational range of the effect. The top edge of the graph represents the To value and the bottom edge of the graph represents the From value. As you can see at the top left of the image below, fairly sharp angles can result. This is due to the fact that a path Spline’s Intermediate Points are included in the calculation of the rotation. The more uniform and closer together the intermediate points lie, the softer the rotation will be. The example at the bottom shows what the Sweep object looks like after the path Spline’s Intermediate Points setting was set to Uniform and its Number value has been raised.

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