5 sided nurbs surface

[MaryBea]

VW 2008, intel iMac OS 10.5.5. I have been using 4-sided nurbs surfaces to design tensile shade sails (all four corner points at different heights). When I convert a 5-sided nurbs curve, with different corner point heights and curved sides, to a nurbs surface the Z positions of the vertices don't correspond with how a fabric surface would react. I can move all the vertices but it is very trial and error. Is there an easier way to create a smooth 3d surface with 5 curved sides and corners of different heights? Many thanks. Bea

[Benson Shaw]

Sorry for no responses after this long time, but here is my stab at it. It is not really easy but results are pretty close to fabric shape. The short story is that you start with a bigger NURBS surface and trim the edges to suit.

Start with a plan view, 2d pentagon. Vertices are your shade pull points.

Convert to 3d poly and raise the z value of each vertex.

Still in Plan, draw two edge NURBS connecting vertices (they converge at one end. the other end is open), and a center NURBS (straight)

Edge curves have proper 3d shape. Raise the mid point z value of the center line to make it curve off the ground plane.

Loft the 3 curves.

In Plan, draw arcs as trim surfaces along each edge and use the Project Tool in Split mode to trim the NURBS Surface.

Switch around in side, top and front views to adjust vertices as nec to make a closer shape to the fabric.

I hope you figured out some way to do this. Mesh may be another way to go.

-B

[MaryBea]

Thank you for the clear explanation! I just had one problem - when I loft the curves I get a group of 2 nurbs surfaces - you can see the join, especially when you start adjusting the vertices. Am I doing something wrong?

Thanks, Bea

[Benson Shaw]

Keep trying!

The loft will result in a group of several surfaces if one or more of the origination curves is not continuous (has corners for instance), or has very sharp curves. If the curves have differing vertex count, that can cause a split/group loft, too.

If you start with 3 gentle curves as shown, your loft should result in one smooth surface.

My file is attached, if the moderators let the 300kb pass. Check all the layers and zoom out to see all the objects & text. Start in Plan on the 3d Setup layer, but explore with the Flyover tool.

-B

[MaryBea]

Very many thanks for your great help - I see what to do.

Bea