Spline Object

Spline Object

This command creates an empty spline object. Like the Polygon object, it is recognizable on screen only by its origin and axes.

You can use this object for the construction of your own splines.

Basics

Curves

Splines are primarily a sequence of vertices, connected by lines, lying in 3D space. The shape of these connecting lines (straight or curved) defines the interpolation. Apart from the direct connection of the vertices with straight, rigid lines, there are other kinds of splines that use an interpolation method where the lines between the vertices are curved instead of straight. These splines have a soft leading edge without sharp corners.

The spline itself is infinitely thin. A spline is not visible when rendered. The spline’s line has no three-dimensional depth, even though it occupies the 3D space. However, many complex 3D objects, among other things, can be constructed in seconds out of these curves by using them with NURBS objects.

After the spline is created it can be pulled along its depth in order to make tube-like objects. You can also rotate a spline around an axis to create objects that have rotational symmetry, such as wineglasses. Or you can construct a skin over several splines, with the finished object simulating the contours on a map. More of these spline-modeling capabilities are discussed in the NURBS section.

Segments

A spline is made from several partial curves, or segments. For example, if you create some text, you will see that only one object is created, even though you typed in several letters. The text object now consists of several outlines — one outline or more per letter.

For example, the word Test consists of four letters; that makes four separate segments. However, another, fifth, segment is also present — the inside of the e is a further spline segment. If this type of element is later extruded to form a 3D object, CINEMA 4D will automatically punch out a hole that is the same size and shape of the internal segment of the e.

A spline converted to a 3D object with holes automatically created.

Holes are formed only if a spline lies completely inside another spline and both form closed curves. If two segments overlap in any way, no 3D object can be formed. If you nonetheless try, strange results are likely.

On the left is a correct arrangement of splines and on the right we see spline segments arranged in an incorrect order.

A spline object can be composed of any number of segments. However, all segments of a spline must have the same settings, e.g. they should be either all open or all closed and all have the same kind of interpolation. So, what is the advantage of a spline with many segments and many separate spline objects? Well, as long as the element is present as a complete, individual object, then all of its points can be modified and edited at the same time.

Let’s return to the text example above. Before you convert the spline to a 3D object, you can bend it e.g. using deformer objects. The tool affects all vertices of all segments equally. Therefore the spline is deformed evenly, as a whole.

The spline was modified before extrusion.

If we have nothing but individual, separate spline objects, then even simple deforming becomes very difficult, if not impossible. As you can see, splines are an extremely important part of CINEMA 4D.

To create a new spline curve:

1. Choose Objects > Spline Object to create an empty spline.
   
2. Select the Points tool (click the Points icon or choose Tools > Points) and select the Move tool (choose Tools > Move).
   
3. Create points for the spline by Ctrl-clicking in each place where you want to create a point. The first point defines the start of the spline.
   If you Ctrl-click on the curve between two existing points, the new point will be placed on the spline between the points.
   If you hold down the Shift and Ctrl keys while clicking, the new point will be created at the beginning of the spline, giving a new starting point.
   If the Close Spline option is enabled and you Ctrl-click the starting point, the spline will be closed.
   You can move points by dragging and dropping them. To select multiple points, Shift-click each point (or use a selection tool).
   

The spline is always created in the view of the active viewport. Bezier splines, B-splines, Cubic splines and Akima splines will be created on the construction plane in the perspective view or on the world planes of the remaining views. With a Freehand spline drawn in the perspective view, the spline will be created on the plane that is perpendicular to the camera direction. In all other views, the Freehand spline will be created on the world planes.

For some operations, such as the aligning of objects along a spline (Arrange command) or the movement of objects along a given curve (Align To Spline tag), the direction of the spline (where it begins and ends) is important. For this reason, the spline is color-coded.

By default, from the first vertex, the starting point, and moving outwards, the curve is colored from white to blue (the end point). The colors of the start and end points can be changed within the preferences. The colors chosen are then changed, in a graduated fashion, between the two points. This colored display is visible only when the Points tool is active.

To create a new spline segment

1. Create a spline as described above.
   
2. Add a new point that will be the start point of a new segment (initially, this new point will be connected to the last point of the previous segment).
   
3. Choose Structure > Edit Spline > Break Segment. The connection to the previous segment is now broken.
   
4. Add further vertices. All new vertices now belong to the new segment.
   
5. You can create further segments.
   

If a spline consists of several segments, then new vertices are always created from the active vertex. If no vertices are active, then new vertices are generated at the last-created segment. If several vertices at different segments are active, new vertices are always generated at the first-created segment.