QCad User Reference Manual

## Splines

CAD Toolbar:

Menu:

Draw - Spline

Command:

?

Options Toolbar:

Description:

Draws spline curves. Non-uniform rational B-Splines (NURBS) with homogeneous weighting factors are the only ones that are currently supported.

Procedure:

1. Choose the degree of the spline in the options toolbar. Supported degrees are 1, 2 (quadratic b-spline) and 3 (cubic b-spline). The higher the degree, the 'smoother' the curve becomes. Degree 1 splines are almost never used.
   Note, that a quadratic b-spline requires at least 3 control points while a cubic b-spline needs at least 4 control points.
2. Check the 'Closed' checkbox in the options toolbar if you want to create a closed spline. Closed splines are continuous closed loops.
3. Specify the control points. After defining the third (for quadratic b-splines) or fourth (for cubic b-splines) control point, a preview will be shown. You can remove the last control point again if it was accidently put in the wrong place by clicking the 'Undo' button in the options toolbar.
4. Click the right mouse button to finish the spline tool.

Figure 32: Open splines with four control points.

Figure 33: Closed splines with the same control points.