by Rhino user Steve Howden

The specific context of this post to the Rhino news group was flattening for fabric, but most of this should apply to compound curve surface development from Rhino.

There are several ways to do this, but first (to make sure we are speaking the same language) let me point out that there are two types of surfaces:

1. Developable, no curvature in one dimension. Examples: cylinders, cones.
2. Double curvature. Example: spheres.

So you have two options:

• Design your bags by creating the seam lines and lofting (developable) between them. Then use _Unrollsrf to get your patterns.
• Or model your shapes using whatever method you like and then projecting or pulling seam lines to the surface and splitting that surface up. This gives you more design flexibility. Note: In V4 there is a very handy tool, _Shortpath, that is good for this. It gives geodesic curves on the surface.

Once you have these split surfaces you can flatten them using one of the available methods for dealing with double curvature (i.e. non developable) surfaces. Note: Any surface flattened in this way will be an approximation, but sensible seaming will minimize this.

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This is free (part of V4). Try both the unrolling directions along U and V to see which gives the best result. Also, watch the dialogue which will tell you what percent change in surface area the unrolling caused. If it tells you that the surface is 65% smaller after unrolling then you know it has all gone horribly wrong.

*Discontinued as of January 31, 2007

Not a free plug-in for V3. This is my current favorite. It gives extremely good results and has the major advantage of giving you a color gradient map that shows how much stretch and compression is needed to create the flattened surface.

Available from: http://www.shipconstructor.com/productsandsolutions/companionproducts/expander.html

For an alternative to expander in V4, see: AdvancedFlattening.

Rather nice standalone program that can read .obj files from Rhino. Suffers from not having a good way to split up surfaces, so you have to do it all first in Rhino, then export and expand. If you don't like the results you have to go back to Rhino, resplit, export again, and re-expand.

Available from: http://laminadesign.com/

Standalone program with a modeling method that does my head in. It does have the major advantage of real time flattening, i.e. change a model in 3D and it instantly updates the 2D patterns. This is brilliant for getting optimum fabric use.

Available from: http://www.touchcad.com/

Note: You cannot get Rhino surfaces into TouchCAD. You have to model in TC.

Not a flattening program per se but it has some nice 3D features which let you take your flat patterns and stitch them together, then simulate how the final product will pull together. You can define the fabric characteristics and seam tension and it gives a very accurate model of the final product right down to seam wrinkles and folds. It is also a complete pattern design, nesting, grading, and CNC cutting controller. We've been using it for ages and love it. Expensive as hell but worth every cent.

I was told yesterday by the CEO that flattening is in alpha and will be available in the next version. Fingers crossed.

Available from: http://www.optitex.com