Hi Will, so just an example with flipping...

Say you are in a polygon modeling program and you create one polygon like this:



Then you add a second polygon here:



And then a 3rd one here:




At this point you have a mesh with 3 polygons. It does not necessarily have its normals oriented towards what now appears as the "outside", you may need to flip it. It depends on how the first polygon was drawn and what direction it happened to start out with.

The polygon modeler doesn't really understand that the first created polygon was supposed to be the front face or the back face or whatever of the final object.

The same thing will happen when working with NURBS surfaces as well - it's not something that is a bug to be fixed, it's something that is part of working with open geometry in any kind of geometry system.

So it is not unexpected or abnormal or a bug that you may need to flip open pieces, it's an expected part of the workflow.

But if you work with solids, it is another thing that you can avoid worrying about because it then does get handled for you.

- Michael