Fold geometry toolbox – Automated determination of fold shape, shortening, and material properties

The Fold Geometry Toolbox (FGT) provides a quick and quantitative shape analysis of generic, two-dimensional single and multilayer fold trains. Fold geometry is described using four basic parameters: fold arclength, amplitude, wavelength, and thickness. Several existing definitions of these parameters are implemented and in the case of thickness a new one is proposed. The advantage of FGT over existing tools is that it uses normalized and parameterized data representations, which ensure that the outcome of the analysis is invariant to rigid-body motions and dilation. FGT can deal with noisy interfaces and implements a new combination of filters that automates the identification of hinges and inflection points, minimizing the user input. In the final step of the analysis, FGT relates the obtained geometry parameter values to mechanical properties and shortening of folded layers. We demonstrate the use of FGT with data from a finite element simulation and a natural case. FGT is open source, written in MATLAB, and comes with a graphical user interface.