Odd Parameterization of Rebuild Command

I’m just curious as to the logic behind the parameterization on the Rhino Rebuild command. The command tends to evenly spread the middle control points, but then put the control points closest to the ends much closer to the edge. So it’s not quite an even parametrization across the entire surface, but certainly not being fit to curvature or anything like that. If there’s not going to be an option to have different parametrization, why not just default it to arc length and keep things even?

@mikko - can you enlighten us?


For curves Rebuild command basically divides it into N equidistant points, and then interpolates a new curve through those points. The resulting curve has a knot at each of those points, and each knotspan is about the same length, so the parameterization is fairly even. You can use InsertKnot or RemoveKnot to study the knot structure. For surfaces the same is done in 2 dimensions.

Was/is there some technical barrier to simply creating curves/surfaces with an arc length point distribution? I mean I get what you’re saying, but the parameterization is kinda like a weird hybrid that doesn’t really help.

And if I’m reading right, it’s basically leveraging the InterpCrv command? Cause that always does the same goofy thing with the oddly spaced points one in from the end.

Control point spacing is not a direct indication of the parameterization. The knot spacing is.

Okay then, what would it take to get a Rebuild command that creates (roughly) evenly spaced control points throughout?

I have no idea.