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| Posizione nel menu |
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| Sketch → Strumenti B-spline → Aumenta di grado |
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| Sketcher |
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| Introdotto nella versione |
| 0.17 |
| Vedere anche |
| Crea B-spline |
Descrizione
Aumenta il grado della B-spline (vedere: B-spline).
Utilizzo
- Selezionare un bordo da una B-spline esistente e premere
Aumenta di grado.
Example
B-splines are basically a combination of Bézier curves (nicely explained in this and this video).
In this cubic B-spline (degree 3) there are 3 segments, meaning 3 curves are connected at 2 knots.
The degree is indicated by the number in the center. See 
Show/hide B-spline degree.
B-spline with degree 3 and 2 knots that each have multiplicity 1.
The outer segments each have 2 control points, the inner segment has none to ensure the knots have multiplicity 1. See this page for an explanation about multiplicity.
Increasing the degree to 4 will add control points without changing the shape of the B-spline:
Same B-spline where the degree was changed from 3 to 4. Note that the knot multiplicity has also increased.
From this result you cannot get back to the initial state of the B-spline by decreasing the degree. Some information is lost when the degree of a B-spline is changed. Decreasing the degree back to 3 leads to this:
Same B-spline where the degree was changed back from 4 to 3. Note that the knot multiplicity has increased again. Depending on the B-spline, the algorithm to decrease the degree may add a lot of knots to preserve the shape as has happened here.
Each segment now has 2 control points and each knot is coincident with an additional control point. The knots have C0 continuity so that the B-spline will get "corners" if you move a control point. The information of a higher continuity is therefore lost. See this page for an explanation about continuity.
Questa pagina è recuperata da https://wiki.freecad.org/Sketcher_BSplineIncreaseDegree