Thanks for your explanations Michael. What I need to do in the end will be a hiking boot very much like this:
http://upload.ecvv.com/upload/Product/20095/China_Men_Hiking_Shoes20095182102462.jpg

The 3D model of the predecessor was made with rhino. So I thought it would also be possible with MOI...
I cannot come up with a plan to make it without spline patching. Is there a better and simpler way?

Cheers,
Rogurt

Hi Rogurt,

> Here´s the scene file

If you turn on surface control points it should help you to see what's going on there:



So note there that the control points are not all one parallel plane slices - the middle row of 3 control points are on a plane but their plane is rotated a bit. It's often that kind of rotation or wobbling of the internal structure of the surface that makes for a bit of a bulging shape where it ends. The same effect does not really create as much problems when you make an extended larger shape instead of separate small patches like this.

The canonical way to build a sphere shape in NURBS is as a surface of revolution and not by Network.

Also working with 3 sided areas can add in more difficulties, since NURBS surfaces are inherently 4 sided things, so to make a 3 sided patch one side is compressed to a point and that often makes for some slightly different shaping behavior in the direction that collapses down like that (although not with Revolve).

It is actually possible to surface your sphere here patch by patch if you use Sweep instead of Network - if you select this curve here as the profile for the sweep:



Then run Construct > Sweep and pick the other 2 adjacent curves for the rails. This will initially generate the same kind of slightly bulged thing like this:



But with sweep for some particular cases like this you can enable the "Maintain tangent" option which will construct the sweep all out of parallel planar sections, which basically avoids wobbling the shapes as the travel along the rails. That will generate the kind of result you were looking for:




If you turn on surface control points for this result you can see the difference:




Also note though that the surface is a lot more complex and dense, with the sections restrained to only be on parallel planes it usually requires a lot more of them to be used to generate a surface that matches close enough to the rails.

So it's not a way that I'd recommend for actually building a sphere - a surface of revolution is more accurate and also lighter at the same time.

But I hope that this may illustrate to you why you get the results that you were confused about - when the surface is marching along in 3D in a totally generic way like with network there is no special restriction for its structure to be all on parallel planes and that kind of general rotation is what causes the kind of bulged shapes at the edges that you were seeing.

I've attached a new version of your 3DM file that was built in octants using this particular sweep method instead of Network.

- Michael

Hi Rogurt,

> What I need to do in the end will be a hiking boot
> very much like this:

That's going to be a very challenging model to create from NURBS - you'll be basically operating outside of the easiest areas of having much of the model defined well by 2D profile curves so you'll instead be needing to work more all with 3D curves and using the most advanced areas of the toolset.

It's a much more complex area to get used to, so it's something that you are likely going to need to invest a lot of time to get good at.

Things that are at that level of difficulty I just generally think can be better off done with a polygon modeler, sub-d modeling with a polygon modeler is much more oriented towards working all with 3D sculpted type shapes moreso than MoI is.


> The 3D model of the predecessor was made with rhino. So
> I thought it would also be possible with MOI...

It might be technically possible to do in MoI, but it's at such an advanced, difficult, and finicky area of NURBS modeling that it has not been a big focus in MoI to target that kind of modeling, since it's generally better handled by sub-d modeling instead.

Also when you get to this kind of advanced surface level of work there are some additional tools that Rhino has that are not in MoI yet for editing surfaces to be smooth to one another, like the MatchSrf command in MoI. So if you need some of those specific kinds of tools you will need to use Rhino in combination with MoI to fill in some of those kinds of functions.

I do want to add those advanced surfacing type of functions into MoI as well, but it has been a much bigger priority for me to focus MoI on the areas where NURBS are actually really easy, pleasant, and quick to use like stuff that can be generated more from 2D drawings.

If you're already familiar with polygon modeling, I'd recommend doing that project using one of those tools instead - basically same as if you were doing highly organic stuff like creature or modeling human faces or things of that nature. When your project does not boil down to recognizable 2D curves that define it well it basically starts to move quite a ways into that organic shape territory, and that's an area where sub-d modeling is much more focused on.

- Michael