Hi mir4ea,

> Michael I think this definition have to be on the first place in tutorial list)
> Because it's how nurbs works on low level.
> Now knowing this, I am sure I'm more confident in nurbs modeling.
> It's peaty a bit that I know it accidentally after half of year of using MOI :)

I've tried to explain it in the FAQ with some illustrations there too... But it's such a different structure than how polygon mesh geometry works that I think it can just take some time and experience with working with surfaces for a while first before it really sinks in.

It's also the reason why you can't just grab any edge that you see and pull it around like you can do in a polygon modeling program, because often times the edges in a NURBS model are set up more like markers that mark some areas of the surface as active and others as holes. The actual surface shape comes from the "underlying surface" and so to modify the shape means modifying that surface's control points and not the "markers".

In a polygon mesh modeler every edge that you see is not just a marker but the edge of a little polygon surface, there is not any concept in a polygon modeler of there being edges that are just "trim markers" instead of being a direct defining part of the surface geometry.

- Michael