Sketcher BSplineIncreaseDegree
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| Menu location |
|---|
| Sketch → Sketcher B-spline tools → Increase Degree of B-spline |
| Workbenches |
| Sketcher |
| Default shortcut |
| None |
| Introduced in version |
| 0.17 |
| See also |
| Show/hide B-spline degree, Decrease B-spline degree |
Contents |
Description
Increases the degree of the B-spline(see B-spline).
B-splines are basically a combination of Bézier curves (nicely explained in this and this video). These curves have degree - 1 control points.
In this cubic spline (degree 3) there are 3 segments, meaning 3 curves are connected at 2 knots
(degree is indicated by the number, indication can be changed using the toolbar button 
Show/hide B-spline degree):
B-spline with degree 3 and 2 knots that each have the multiplicity 1.
The outer segments have each 2 control points, the inner one none to fulfill the constraint that the knots have multiplicity 1. (see this page for an explanation of the multiplicity)
Increasing the degree will add control points so that the shape of the spline is not changes. Therefore segments will be added. For our example you see a lot of new spline segments with each one control point and the shape of the spline has only slightly been changed:
Same B-spline where the degree was changed from 3 to 4. Note that also the knot multiplicity was increased.
If you take this result and decrease the degree, you cannot get the initial state of the spline because information was lost by the increase of the degree. For our example decreasing the degree again leads to this:
Same B-spline where the degree was again changed from 4 to 3. Note that the knot multiplicity was not also decreased but increased again.
Usage
- Select an edge from an existing B-spline, and press
Increase B-spline degree.
Sketcher
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- Sketcher B-spline tools Show/Hide B-spline degree, Show/Hide B-spline control polygon, Show/Hide B-spline curvature comb, Show/Hide B-spline knot multiplicity, Convert Geometry to B-spline, Increase degree, Increase knot multiplicity, Decrease knot multiplicity
- Sketcher virtual space Switch Virtual Space
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