An energy-driven approach to linkage unfolding

We present a new algorithm for unfolding planar polygonal linkages without self-intersection based on following the gradient flow of a “repulsive” energy function. This algorithm has several advantages over previous methods. (1) The output motion is represented explicitly and exactly as a piecewise-linear curve in angle space. As a consequence, an exact snapshot of the linkage at any time can be extracted from the output in strongly polynomial time (on a real RAM supporting arithmetic, sin, and arcsin). (2) Each linear step of the motion can be computed exactly in O(n2 ) time on a real RAM where n is the number of vertices. (3) We explicitly bound the number of linear steps (and hence the running time) as a polynomial in n and the ratio between the maximum edge length and the initial minimum distance between a vertex and an edge. (4) Our method is practical and easy to implement. We provide a publicly accessible Java applet [1] that implements the algorithm.

• Type: Conference
• Year: 2004
• Where: COMPGEOM
• Authors: Jason H. Cantarella, Erik D. Demaine, Hayley N. Iben, James F. O'Brien
• Keywords: COMPGEOM 2004, Linear Steps, Planar Polygonal Linkages, Real Ram