The interpolation curve used by Grasshopper

Hello world, a quick question about the interpolation curve.

I have tried finding this information in the GH Primer as well as in previous discussions, but no luck.

What type of curve is the interpolation curve used by grasshopper? I want to be able to predict the consequence of changing its curve degree.

I have found some articles describing B-splines and the differences between the degrees, but I need to confirm/disconfirm that this is the curve used :)

If you know of any source of information on this, I'd be very thankful:)

Thank you!

Replies to This Discussion

Permalink Reply by Daniel Eika on June 28, 2012 at 6:33am

Any response on this would help me out alot. I thank you in advance for any time spent responding on this discussion.

Permalink Reply by David Rutten on June 28, 2012 at 6:44am

It's a nurbs curve. Just like the Rhino _InterpCrv command.

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Daniel Eika on June 28, 2012 at 8:32am

Thank you. But isn't an Interpolated curve by definition not a NURBS curve? Grasshopper Primer p 69 implies that it is not a NURBS curve (except for w. degree 1, which makes sense :)).

Permalink Reply by David Rutten on June 28, 2012 at 8:56am

Every freeform curve in Rhino is a nurbs curve. There is no other kind of curve that can handle freeform shapes in Rhino. Well, that's not true, we also have Beziers and Polynomials, but they are purely SDK curves, they are never inserted into the 3dm document. The only curves that you can encounter in the document are:

LineCurve
PolylineCurve
ArcCurve (which handles both arcs and circles)
NurbsCurve
PolyCurve (which is just a sequence of other types, strung together)
ProxyCurves (for example Brep edges)

When you interpolate a set of points Rhino will invent a Nurbs curve that intersects all these points. The control-points for this curve may be way out in space, there is no constraint on where they can and cannot be positioned.

There are some options though. Degree of course is one. Knot-spacing is another. It is also possible to constrain the start and end tangent when using the interpolater in code.

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Daniel Eika on June 29, 2012 at 5:16am

Thank you, great and precise info, it will be of much help! :)

I assume then that by increasing the degree of the interpolation, you amongst other things increase the number of controlpoints defining the curve; allowing it to "wiggle" more?

RSS