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Surface Surface Flattening > Unroll Developable Surface 
The UnrollSrf command flattens (develops) a surface or polysurface with curvature in one direction to a planar surface.
Commandline options  

Explode 
YesThe resulting surfaces are not joined. NoThe resulting surfaces are rejoined along the same edges that were joined in the original polysurface. To specify where the unrolled polysurface will split

Labels 
Determines whether or not matching numbered dots are placed on the edges of the selected object and the resulting objects. 
KeepProperties 
Determines whether or not the selected object's properties are copied to the resulting object. 
RelativeTolerance 
Compares the maximum deviation of a curve from a line between its endpoints to the Relative Tolerance * length of the curve. If a curve is 10 units long and the relative tolerance is .01, the maximum deviation is compared to 0.1. If the line is 100 units long, max deviation is compared to 1. 
Rhino has commands to create and unroll developable surfaces with holes and marking curves.
Developable surfaces are surfaces that can be formed by rolling a flat sheet of material such that the material does not stretch, tear, or wrinkle. Examples of this type of shape are cylinders, cones, and some steel ship hulls.
Picture trying to make your surface out of aluminum foil. If it crinkles or tears as you try to bend it into position, the surface is not developable. A sphere is an example of a surface that are not developable (try wrapping an apple with aluminum foil). So are most of the shapes on car bodies and most modern car windshields.
Surfaces must still be linear in one direction for UnrollSrf to unroll them. You could lay a ruler along the surface and it would touch the surface from one edge to the other. These are called ruling lines.
Because these surfaces are linear in one direction, the Gaussian curvature is zero at every point on the surface. If the Gaussian curvature is not zero, Rhino will not be able to unroll the surface. If the surface is not linear in one direction, Rhino will not be able to unroll the surface.
Since developable surfaces cannot be created from just any two curves, results from a developable style loft can be unpredictable. Curves of similar shape without kinks work best.
You can use Gaussian curvature analysis to determine which areas of a surface are not developable.
These developable surface tools work best for designing airfoil and hydrofoil type surfaces. They were not designed to be used for bending and unfolding sheet metal like duct work or for developing fabric patterns.
When building a developable surface, you can get very different results depending on the complexity and similarity of the two edge curves. It is best if they are as simple as possible and have the same parameterization.
Picking different ends of the curves can give different results. You can sometimes combine the different results to get a better developable surface.
A developable surface is not necessarily a fair surface.
It is possible to make a developable surface that unrolls with a difference in area and ruling lengths from the 3D surface. It is easy to miss the warning Rhino gives.
You can unroll surfaces that are not developable.
Rhino does not have any method of making a surface a bit more or less developable. Some programs have a way of spreading out the concentrated fans of rulings that often occur, thereby smoothing the surface. Since metal, especially aluminum, has some elasticity, you can deviate quite a bit from a mathematically correct developable surface and still plate it up. Some builders that use developable surfaces in their models, expand the plates, and then add up to 1inch chord depth of radius to the flat sides in the sections to make the plate "taut." The expanded plates fit up to the changed sections. They have not figured out how to get this "blow" into their 3D models, though.
One way to approach the problem is to use the CurvatureAnalysis command to analyze the Gaussian curvature as a guide to surface creation instead of the developable loft. But there is no way in Rhino to expand surfaces created this way (unless they happen to meet the requirements for the UnrollSrf command).
The goal of many designers is to obtain flattened, twodimensional patterns from their threedimensional designs. The threedimensional surfaces are analyzed using Gaussian curvature analysis and classified into two types of surfaces: developable and nondevelopable.
Developable surfaces can be flattened using exact solutions. These are surfaces like cones, truncated cones, and cylinders.
Spheres and other surfaces, that have compound curvature, cannot be unfolded or “developed” accurately without knowing something about the characteristics of the material (amount of stretch available and more.)
Nondevelopable surfaces have compound curvature, that is, curvature in two directions. Flattening or developing these surfaces requires stretching or shrinking of the material used.
The Curvature command will show the curvature curve as you move your cursor over the surface. The nondevelopable surface show the curvature with two arcs, to illustrate the compound curvature. Developable surfaces will show curvature with a single arc and a line, illustrating the curvature in a single direction.
The unrolling or flattening of nondevelopable surfaces is based on complex transformation matrices that factor in material characteristics and transform the surface on to the xy plane as a twodimensional boundary. The material’s characteristics help determine stretch that material will experience to produce the shape.
It is helpful to imagine cutting and folding paper. A developable surface can be folded or rolled from a sheet of paper. Clearly, a sphere does not fit that criterion. A sphere of sorts can be constructed from a series of developable panels and can be developed panel by panel, but of course it will not be a true sphere, but an approximation. In short, if a surface can be constructed with paper, then it is determined to be developable and Rhino should be able to unroll it. If you need a sheet of rubber to make the 3D shape, then it is nondevelopable and the UnrollSrf command will not unroll it.
The Smash command makes an approximate 2D development of surfaces that have compound curvature. This command can be used to deal with fabrics that have a certain amount of flexibility and stretch.
The UnrollSrfUV command flattens (develops) a surface or polysurface while preserving the UV of the input surfaces.
Commandline options  

Explode 
YesThe resulting surfaces are not joined. NoThe resulting surfaces are rejoined along the same edges that were joined in the original polysurface. To specify where the unrolled polysurface will split

Labels 
Determines whether or not matching numbered dots are placed on the edges of the selected object and the resulting objects. 
Flatten a surface without restriction to singledirectional curvature.
Flatten a nondevelopable (curved in two directions) 3D mesh or NURBS surface into a flat 2D pattern.
Rhino for Mac © 20102017 Robert McNeel & Associates. 24Oct2017