“…The 2D and 3D Classification step in the previous section can be used to derive several class averages, each of which can be distinctly used to build 3D models with variations showing the differences in structures that contribute to heterogeneity. Currently, there are several mathematical methods [6] (such as Multivariate Statistical Analysis, Maximum Likelihood Estimation, 3D-Covariance, K-Means Clustering etc.) currently attempted with partial success.…”