I’m doing a lot of surfacing of laser scanned data these days, and my workflow tends to favor point editing surfaces over creating lots of input curves. This keeps my surfaces clean and simple, and lets me edit/match after the fact. Essentially what I will do is start with a half way decent surface that matches my laser scanned data, and then point edit as needed. If I feel that I don’t have enough control, I will up the degree of the surface, so quite often I’ll start with a degree 3 surface, do a little tweaking, go to degree 4, tweak a little more, then polish if off at degree 5. I’m just upping the degree without changing the surface by using the Shape plugin, but this could be done just as easily with Rhino’s ChangeDegree. Sometimes, to hit the target deviation from the reference data, I will even start to add additional spans - so maybe I end up with a surface that is degree 5, 3 spans or the like. Anyhow, the problem I’m having is in the addition of control points/spans. My understanding of NURBS math is that:
For any given curve/surface of N control points, the same shape can be represented with N+1 control points.
Is this correct? If so, then for a curve that is say degree 5 with 6 points (single span), the same curve can be represented with say 8 points, or 10 points, right?
Using the InsertKnot command, and using the Automatic option works in this way the first time you bump up the control point density, but after that it starts to add points at a geometric rate. So, for every time I use InsertKnot, the control point count will go: 6->7->9->13 and so on. What I want is something that will go 6->7->8->9 instead - if such a thing can be done without making the surfaces non uniform.
And, just to nip it in the bud, no, Rebuild won’t work here - it will change the shape. What I’m looking to do is add control points at a rate of N+1, without changing the shape or making the curve/surface non uniform.