You misuse “NURBS” with “patch”. While “XNurbs” is based on NURBS (like “Blend surface”, “Network surface”, “Sweep 1 rail”, “Sweep 2 rails”, “Loft” and many others"), in essence it’ a patch tool. A good patch tool that’s comparable to the patch tools in some other CAD programs. And much better than Rhino’s own “Patch” tool.
You mentioned that I “don’t understand the basic concept of NURBS”. Were not your car front bumper, jet hull and mouse body examples shown here to advertise the capabilities of XNurbs to combine multiple patches, in order to build whole models? As you know, I filled the middle area of the Y-branch model with several surfaces build with a few basic Rhino tools. The same should be possible with XNurbs, too. The latter could use curves as boundary constraints to G0 (exactly what I did while using Rhino’s basic “Patch”).
Your description of XNurbs is a bit loose, and, in my opinion, it’s more safe to advertise it as an advanced patch tool that could deal with many (but not all) scenarios where other NURBS tools fail to deliver the same results. By providing two different 3d models above, I already proved that some basic Rhino tools are far superior in the same circumstances where XNurbs showed obvious weakness. There is nothing wrong with that, because it’s natural for a patch tool to be less accurate and smooth than well-balanced “Blend surface”, “Sweep 2 rail” or other types of NURBS surfaces that were additionally improved with control point manipulation and “Match surface”.
I guess that you don’t understand the difference between a linear system and a non-linear system.
That’s right, I have no idea what those two are about. However, I pretty much understand what’s a smooth flow of the whole model, which is the primary reason for using NURBS over mesh modeling for manufacturing purposes. Both, the car bumper and mouse body of your examples have inconsistent wavy areas that will never meet the requirements for manufacturing.
You are welcome to use my 3dm model from my previous post and follow the guides that I wrote next to each 3d model, describing the modeling process step by step.
Are you willing to share the 3d model of the car fender that you posted on your website as an example of the capabilities of XNurbs over other NURBS tools? I would like to examine it and, if I have some free time, I will send you my own version with better surface quality made entirely with basic Rhino tools.