Three open problems on folding/unfolding are discussed: (1) Can every convex polyhedron be cut along edges and unfolded at to a single nonoverlapping piece? (2) Given gluing instructions for a polygon, construct the unique 3D convex polyhedron to which itfolds. (3) Can every planar polygonal chain be straightened?

A band is de ned as the intersection of the surface of a convex polyhedron with the space between two parallel planes, as long as this space does not contain any vertices of the polyhedron. An unfolding of a given band is obtained by cutting along exactly one edge and placing all faces of the band into the plane, without causing intersections. We prove that for a speci c type of band there exists an appropriate edge to cut so that the band may be unfolded.

This thesis contains new results on the subject of polygonal structure reconfiguration. Specifically, the types of structures considered here are polygons, polygonal chains, triangulations, and polyhedral surfaces. A sequence of vertices (points), successively joined by straight edges, is a polygonal chain. If the sequence is cyclic, then the object is a polygon. A planar triangulation is a set of vertices with a maximal number of non-crossing straight edges joining them. A polyhedral surface is a three-dimensional structure consisting of flat polygonal faces that are joined by common edges. For each of these structures there exist several methods of reconfiguration. Any such method must provide a well-defined way of transforming one instance of a struc-ture to any other. Several types of reconfigurations are reviewed in the introduction, which is followed by new results. We begin with efficient algorithms for comparing monotone chains. Next, we prove that flat chains with unit-length edges and an-gles within a wide range always admit reconfigurations, under the dihedral model of motion. In this model, angles and edge lengths are preserved. For the universal

We study algorithmic aspects of bending wires and sheet metal into a specified structure. Problems of this type are closely related to the question of deciding whether a simple non-self-intersecting wire structure (a carpenter's ruler) can be straightened, a problem that was open for several years and has only recently been solved in the affirmative. If we impose some of the constraints...

Abstract not found

Origami is the centuries-old art of folding paper, and recently, it is investigated as computer science: Given an origami with creases, the problem to determine if it can be flat after folding all creases is NP-hard. Another hundreds-old art of folding paper is a pop-up book. A model for the pop-up book design problem is given, and its computational complexity is investigated. We show that both of the opening book problem and the closing book problem are NP-hard. Keywords: Computational Complexity, Origami, Paper folding, Pop-up book. 1

The Unfolding Problem can be succinctly described as “How to peel an orange... no matter what shape the orange is. ” It is the question of how to ‘unwrap ’ a 3D polyhedron, breaking some of its edges or faces so that it can be unfolded into a flat net in the 2D plane. From there the flattened net of faces might be printed out, cut from paper or steel and folded to recreate the virtual model in the real world. In 1525 the artist Albrecht Dürer used the term ‘net ’ to describe a set of polygons linked together edge-to-edge to form the planar unfoldings of some of the platonic solids and their truncations. Dürer used these unfoldings to teach aspiring artists how to construct elemental forms, but today the applications for solutions to the unfolding problem lie in a broad range of fields, from industrial manufacturing and rapid prototyping to sculpture and aeronautics. In the textiles industry, work has already begun in computing digital representations of fabric and trying to flatten those representations to optimize seam and dart placement [MHC05]. There has been similar work in the fields of paper-folding [MS04] and origami [BM04] and even ship and sail manufacturing. Advances in robotics and folding automation [GBKK98] have brought with them a new need for faster, more robust unfolding methods. If a polyhedron can generate a net which is not self-intersecting, solely by breaking a subset of its edges and flattening the join angles of those which remain, then it is called edge-unfoldable or developable. At present, it is strongly believed–but not yet proven–that all convex surfaces are developable. In counterpoint, examples are easily found of non-convex surfaces which are cannot be edge-unfolded, but no robust solution yet exists for testing whether or not a given mesh will prove to be developable.