Hi Dex, for your case it looks like you want something like this:

2D profile:



Extruded:



The extrusion will contribute the "side walls" to the end result.

Then for the front and back surfaces, you want to construct a simplified surface that extends out across the entire shape, here done with some profiles:



Then Loft with "Loft style = Straight":



Use boolean difference to cut the extruded shape up:



Discard these excess outer pieces:



Now you will have a solid result that combines the side walls from the extrusion and the front/back shaping from the cutting objects:



So the kind of key element is to not try to "fill in" surfaces to an irregular boundary. For the NURBS modeling technique you want to have simple relaxed surfaces that extend all the way across a shape and then use booleans to impose a more complex boundary on them rather than trying to construct a surface directly to a complex boundary.

Also see here for some tips for people coming from a poly modeling background:
https://moi3d.com/forum/index.php?webtag=MOI&msg=4865.2

- Michael

Hi SUIYAN,

re:
>（This is a boundary surface problem, and there is no corresponding processing tool in Moi.
> In Rhino, you should use the patch tool and then trim it. Please take a look at the pictures
> and demonstrate the process of gif.）

That's something that can be useful in certain cases but it's usually a better modeling technique in NURBS to form extended simplified 4 sided surfaces and then form the final boundary by a boolean operation.

- Michael

Appreciate the quick response guys! I will try these methods out. Couldn't be more grateful, you've been a great help. Thanks!

HI Michael

非常认同，我在#3的讨论中也表达了这样的意思。不过人们更倾向于基于模型原本元素的直接工具，所以我的演示更倾向于此。（I completely agree, and I also expressed this idea in the discussion of # 3. However, people tend to use direct tools based on the existing elements of the model, so my presentation is more inclined towards this.）