Hi Bravlin, often it is not feasible with NURBS to smooth things out using control point editing because of how trim curves and "underlying surfaces" work.

When you do a boolean operation, surface control points do not change at all, instead the trim curves on surfaces are what changes. Trim curves mark areas areas of a surface as holes and in a model with trimmed surfaces you generally can't manipulate surface control points without opening up a hole.

There is some illustration of that here:
http://moi3d.com/faq#Q:_Why_does_show_points_work_for_some_objects_but_not_others.3F

It's a very different type of structure than polygon modeling.

- Michael

So that's why boolean great in NURBS and such a crap in poly modeling.


So the more NURBS-like approach is to build shapes like so ?

Create profile curves, extrude curved surfaces, manipulate points (in this example i
use flow as deformer to bend surfaces) to get shapes you want. And trim it in the end.

Yes you arrive to the Nurbs spirit!

Micro deformation is Polymodeling
Macro deformation in Nurbs modeling! ;)

Hi Bravlin, yup that is correct - with polygon booleans where there isn't any concept of an "underlying surface", things get fragmented into little bits pretty easily.

With NURBS modeling that doesn't happen or at least happens much less frequently and that's a major factor for why booleans with NURBS work well.

There are some other things too like it helps in many situations that NURBS can represent things like an exact sphere with one surface instead of lots of little pieces and then intersections between a sphere and a plane can be handled as a special case with an exact result.

The tradeoff is that trim edges do not necessarily align with the control point structure of the underlying surface and so you can't modify an object by pulling edge points around like you can in poly modeling except in special cases.

So that also means that if you're not using booleans in your NURBS modeling approach you are also not really leveraging the strongest area that it offers.

- Michael

Q_04:
Hi guys. Got another question.
Today it's not about surfaces and shapes.
It's about proportions and scale. I have this kind of a bended shape. It was bent by "Flow" deformer.
Now it has become necessary to make this shape thinner. But if i use scale operator we lose src proportions of this shape.
I assume that Flow operator may help with it. But i can't understand which surface to use for such case.
I don't have src surfaces that i used for shape bending.
If scale operator can solve this problem i dunno how to use it right?

Hi Bravlin, it's usually best to do such edits on your unbent shape and then do a new Flow with your updated object.

It is possible though to do a kind of "scale from center path" operation with Flow, to do that you would make a Sweep of a line profile:


Along a central rail curve:



That will be the base surface for the flow. Then make a narrower sweep surface using a shorter line along the same rail, that will be the target surface for the Flow. An example result is attached.

- Michael