Different kinds of splines.

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CVH
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Location: Belgium; Antwerp

Different kinds of splines.

Post by CVH » Sat Aug 25, 2018 10:05 am

Andrew,

Still version 3.21.1.0 ; Win7 32bit.

In QCAD we can draw splines by fit-points and control-points.
An example of those are in the example included.

On investigation the spline in the post of benjamindahl is a different kind:
https://www.qcad.org/rsforum/viewtopic. ... 859#p21518

Stepping through the points:
-fit-points: steps from fit-point to fit-point. Start- and end-point and fitpoints are knots on the curve.
-control-points: steps from start-point over control-points (not necessarily on the curve) to end-point.
The knot points can be found on the curve as 'intersections'.
-benjamindahl: from the start-point every thirth control is a knot-point.
Knot-points are on the curve and also found as 'intersections'.
Two references in between two knots are vectors and not necessarily on the curve.
It seems this is more like a string of bezier segments.

What is the difference? How are they named?
Can the third kind (knot-vector-vector-knot-....) be constructed with QCAD?

Regards
CVH
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Text Explode Spline 2 linesegments.dxf
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andrew
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Joined: Fri Mar 30, 2007 6:07 am

Re: Different kinds of splines.

Post by andrew » Mon Aug 27, 2018 11:53 am

CVH wrote:
Sat Aug 25, 2018 10:05 am
What is the difference? How are they named?
The difference is the knot vector which is also part of the spline definition.
CVH wrote:
Sat Aug 25, 2018 10:05 am
Can the third kind (knot-vector-vector-knot-....) be constructed with QCAD?
No.

CVH
Premier Member
Posts: 169
Joined: Wed Sep 27, 2017 4:17 pm
Location: Belgium; Antwerp

Re: Different kinds of splines.

Post by CVH » Mon Aug 27, 2018 12:24 pm

So the third kind is suported if originated from 3d party?

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andrew
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Re: Different kinds of splines.

Post by andrew » Mon Aug 27, 2018 6:42 pm

Knot vectors are imported as they are stored in DXF but cannot be changed in QCAD.

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