How to convert "online" to "oncurve"

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Permalink Reply by Giulio Piacentino on June 8, 2009 at 3:11am

I think you could use the "new OnLineCurve(line)" and then use it directly as the OnLineCurve is a OnCurve?

"Public Class OnLineCurve
Inherits OnCurve
Inherits IOnLineCurve"

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Permalink Reply by Damien Alomar on June 8, 2009 at 9:34am

Guilo is correct, but I think that a further explanation on these classes will be helpful. The OnCurve class is an abstract class which means that I don't really ever have an OnCurve and I can't create an OnCurve directly. Generally abstract classes are classes that contain common functionality between other classes. In this case, OnCurve implements a number of functions that are necessary for all of the other curve classes, such as OnNurbsCurve, OnLineCurve, OnPolyCurve, etc. to use. In cases where a given function has an OnCurve as an input, it means that I can use any of those classes that derive from OnCurve within that function.

There are several curve types in the Rhino SDK that do not derive from OnCurve, such as OnCircle, OnEllipse, OnLine, OnPolyLine, etc. In some cases, such as OnLine and OnPolyLine, then have a corresponding class that does derive from OnCurve that generally has the word "curve" after it, so OnLineCurve and OnPolyLine curve. For curve classes that are not derived from OnCurve, yet do not have "curve" counter parts, you can still create an OnCurve derived curve from those classes. Almost all of those non OnCurve classes have a function called GetNurbsForm. With this function you can convert one of those non OnCurve classes to a OnNurbsCurve and use it as you wish.

I know that this is probably a little confusing, but its definitely useful information.

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Permalink Reply by Damien Alomar on June 8, 2009 at 9:41am

Here's a little example of how to get a nurbs form from a non OnCurve class...pretty straight forward.

Dim ellipse As New OnEllipse (OnUtil.On_xy_plane(), 1, 2)
Dim nurbsCrv As New OnNurbsCurve ()

ellipse.GetNurbForm(nurbsCrv)


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Permalink Reply by Giulio Piacentino on June 8, 2009 at 12:22pm

Thanks for the background information. It's very nice to see how things are actually built.

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