Sphericity and roundness computation for particles using the extreme vertices model

•A method to define the orientation based on Oriented Bounding Boxes (OBB).•Compute an OBB using the Extreme Vertices Model (EVM).•An EVM-based method to compute a true 3D roundness index.•Study of correlation between the developed methods and those reported in the literature.•A complete analysis of a real silica nano-dataset applying the proposed methods. Shape is a property studied for many kinds of particles. Among shape parameters, sphericity and roundness indices had been largely studied to understand several processes. Some of these indices are based on length measurements of the particle obtained from its oriented bounding box (OBB). In this paper we follow a discrete approach based on Extreme Vertices Model and devise new methods to compute the OBB and the mentioned indices. We apply these methods to synthetic sedimentary rocks and to a real dataset of silicon nanocrystals (Si NC) to analyze the obtained results and compare them with those obtained with a classical voxel model.