Seam Edge ?

 From:  Michael Gibson
2260.5 In reply to 2260.4 
Hi Anis - all closed NURBS surfaces have a seam edge in them.

SolidWorks may have some kind of method where it automatically hides them or something, but any closed single NURBS surfaces that SolidWorks creates will also have a seam edge as well, it is something that is fundamentally in the definition of a NURBS surface.

I think that SolidWorks may tend to create closed surfaces as 2 joined halves, which does avoid seams though but creates 2 surfaces instead of 1 single surface.

> What is the benefit of seam edge ?

It allows for a single NURBS surface to be a closed shape, like for example a cylinder or a sphere.

Every NURBS surface has an internal UV layout as if it were a rectangular sheet.

It is possible to "pinch together" some edges of this sheet to make a pole region, for example at the top and bottom pole of a sphere - those are areas in the surface where an edge of the rectangular sheet has been collapsed into a single point, the control points of that edge of the surface are stacked up on top of each other in the same 3D location.

Then for making a closed surface, that will involve a seam edge - this is like if you took a rectangular sheet of paper and rolled it into a tube - the tube will have one end of the sheet of paper touching the other end - that is what makes a seam edge.

You can avoid seam edges if you also avoid closed single surfaces.

You cannot avoid seam edges on closed NURBS surfaces, because that like asking for something like "give me some salt, but make sure it has no salt in it". A seam edge is part of the fundamental definition of a single closed NURBS surface.

- Michael