Surface Modeling Basics and Troubleshooting

 From:  Michael Gibson
4751.19 In reply to 4751.16 
Hi Jops,

> but there are quite some things that I miss interpreted.
> I for example thought that if you use one and the same
> spline for 2 surfaces that they would match together.

Well, that actually should be the case - or at least the stuff generated from the same curves is supposed to be close enough to be joinable.

But some kinds of surface creation methods involve some kind of refinement of the generated surface until it hits a certain level of accuracy - in MoI v1 and v2 the Network command uses a somewhat looser tolerance than the other commands (because in some situations with a lot of generator curves it can make a really pretty dense surface), so it was possible for things built by Network off of the same curves to be just slightly out of Join tolerance.

That's fixed in the current v3 betas, but for v2 a workaround is to scale the objects down by 1/10 in size and then do the join.

So it is basically a bug in Network that's been fixed in v3.

You were not wrong with that idea really - and pretty much any other command other than Network should behave the way that you were expecting.

Right now I have not really focused so much on the workflow of building your entire model out of a whole lot of side-by-side networks, because that's kind of more advanced workflow and doesn't really leverage the greatest convenience factor of leveraging 2D curves and solids which is really where NURBS modeling has its greatest strengths.

If you want to build a shape entirely through a whole ton of Network surfaces, it can be kind of a sign that the model may have been better off build in polygons anyway - it can be difficult to get something built in a patchwork way like that to be all smooth, while polygon sub-d modeling has a nice way of smoothing and melting down a patchwork of connected polygons.

> But as I understand your advice. never handle with something
> different than closed shapes. and use trims and booleans with it.
> doublecheck if the result is a closed shape again.

Yup, that's the idea - you certainly can temporarily break things into individual surfaces for particular situations, but if you're only drawing 100% 3D swoopy curves and never doing any trims or booleans on solids, it's probably a sign that you're not really using the boolean and 2D curve toolset to its best advantage.

> Is there a way to check whether something is a closed shape?

When you select the shape, look at the object type indicator inside the object properties panel in the upper-right area of the main window. It's to the right of the object name. If that reads "solid" then it means you have a closed shape. If that says just "surface" or "joined surface" that means you have a non-solid (either just one surface or several surfaces joined together but not fully closed off).

If you do not have a solid then you can use the script in the message above in this thread to highlight the edges which are not joined between 2 surfaces, that will show you where the openings are.

> and the secons thing I learned: If you ever have a batch of
> single surfaces that you want to connect. try it in different scales.

Yup, although that's basically a workaround, but it will work. That's because when you scale objects down the gaps between the surfaces also shrink along with the whole object scale, and once 2 surface edges are within 0.005 units of one another that will allow them to be joined.

- Michael