Splines are types of smooth curves that are created according to the method chosen to interpret the points that are indicated on the screen.
In Autocad, a spline is defined as a "rational Bezier-spline non-uniform curve" (NURBS), which means that the curve is not composed of arcs of circumference, nor elliptical arcs. It is a smoothed curve that, of course, helps us to create designs of curved pieces that escape the geometry of simple objects. As you have already imagined the reader, many of the forms of vehicles, for example, as well as that of many ergonomic devices, require the drawing of this type of curves. There are two methods to build a spline: with adjustment points or with control vertices.
A spline with set points necessarily passes through the points that are indicated on the screen. However, the "Knots" option allows you to select different mathematical methods for spline parameterization, which can generate slightly different curves for the same points.
In turn, the "toLerancia" option of the command determines the precision with which the curve will adapt to the marked points. An adjustment value equal to zero will cause the curve to pass strictly through said points, any other value will "move away" the curve from the points. Let's see the construction of a spline with setpoints but with different tolerances.
You may have already noticed that when starting the command we have the option "Method", which allows us to switch to the second method to create splines, that is, using control vertices, although in turn we can select this method directly from its button in the Options.
Splines created with control vertices are generated through points that, between them, generate temporal lines of a polygon that will determine the shape of the spline. The advantage of this method is that these vertices offer greater control over spline editing, although for editing it is possible to switch a spline of set points to control vertices and vice versa.
Although spline editing is the subject of the 18 chapter, we can say that by selecting a spline, we can use its triangular grip to switch the display of its fit points or control vertices. We can also add some, adjust or delete them.