The B-Spline has two modes
- B-Spline by Control Points
- Periodic B-Spline by Control Points
The B-Spline forms a curved segment that may have two endpoints.
![](https://i0.wp.com/www.freecad.info/wp-content/uploads/2020/06/Selection_701.png?fit=300%2C263&ssl=1)
The Periodic B-Spline will always join the endpoints.
![](https://i0.wp.com/www.freecad.info/wp-content/uploads/2020/06/Selection_699.png?fit=300%2C263&ssl=1)
To use the B-Spline tool :
Step 1.) Create a New Sketch or Edit an existing Sketch.
Step 2.) Select the B-Spline tool from the Sketcher Toolbar
Step 4.) Click the Starting Point ( Vertex ) on the Sketcher plane.
Step 5.) Click once for each additional Control point.
Step 6.) Click once for last control point
Step 7.) Press ESC or Right Click to exit “Adding Control Points”
To add Control Points ( Knots ) to the B-Spline
The Sketcher does not allow for individual placement of knots, it allows an increase in knot “multiplicity”. Using the Increase Knot Multiplicity tool one can add Control Points. The number is increased by one and the B-Spline is sub-divided accordingly