Hi Guys,
this is my second thread!

I try to know how create a smooth surface via curve and NURBS but I can't find the true way.

Here an explicative image where I compare polygons, sds and nurbs.

On every NURBS surface there is an evident error of continuity.

What am I doing wrong?

Hi highlander, it looks like the problem is creating separate surfaces in a "patch by patch" manner rather than making a single larger surface.

Can you post the .3dm model file so I can take a better look at it?

Is there supposed to be a hole in the middle or is the opening to make a flattened spot?

Probably in either case you would probably want to initially make a large extended surface and then cut out that area later rather, it is difficult to make a good smooth surface when your curves have interrupted or irregular shaping like that.

One of the key things for NURBS modeling is to make extended larger forms and then things like holes and other localized features are formed by cutting it with boolean operations rather than trying to construct a shape going around a hole as you would in sub-d/poly modeling.

There are some tips here for people coming from a poly modeling background, they may be helpful:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4865.2

- Michael

about the bottom piece

here with loft ( up ) ( 3 curves )

and with network ( down ) ( 5 curves ) ( maybe much fine ) you can control everything with handles .. change orientation etc ...

don't understand the problem on your other piece ... you want a regular depression in the middle of the piece ?

about the up piece if you want a regular depression

the best way is to filet the initial profile

with a network idem everything can be controlled

In my experience it is complicated to obtain surfaces with continuity with NURBS modeling programs, and the subdivision surfaces that I use in an extensive way solve many problems and difficulties, it is in the intrinsic nature of NURBS that allow great precision but you can certainly not compare the method of work between subdivided surfaces and Nurbs, Moi3D is wonderful but you must also consider that to obtain continuity you will have to work a lot with the surfaces and construction plans.

Hi,

I try to explain in deep the problem about continuity.

I want to recreate a neck of a bass with loft "loose" and profile "refit" and this is the best form that I'm able to realise.

There are some artifacts in the mesh, especially at the end in round part.

Are there any tricks or techniques to resolve these problems?

Hi highlander, the artifacts come from trying to generate too much all in one single surfacing operation. In general one surface should correspond to one broadly shaped smooth area. Things like the tight bends on the edges should usually be done as a fillet operation later rather than trying to incorporate it into the loft.

If you can post a .3dm model file with your current model that would help to try and give you some more feedback on it.

- Michael

Hi highlander some tutorials and other threads you may want to check out:

https://youtu.be/wLaPAeKPuqA
http://moi3d.com/forum/index.php?webtag=MOI&msg=8938.1
http://moi3d.com/forum/index.php?webtag=MOI&msg=8883.1
http://moi3d.com/forum/index.php?webtag=MOI&msg=3618.1
http://moi3d.com/forum/index.php?webtag=MOI&msg=2145.1
http://moi3d.com/forum/index.php?webtag=MOI&msg=4713.1
http://moi3d.com/forum/index.php?webtag=MOI&msg=3446.1

- Michael

Hi Micheal, as requested please find attached 3dm file.

Thanks!

Now I try to learn something!