“…Recently, statistical methods that use eigenvalue-based 3D feature values are becoming popular (West et al, 2004, Rusu, 2010, Toshev et al, 2010, Demantké et al, 2011, Weinmann et al, 2013, Weinmann et al, 2014, Dittrich et al, 2017, He et al, 2017. In these statistical methods, the 3D feature values are defined based on the eigenvalues of the local 3D covariance matrix, which is also called the 3D structure tensor (Jutzi, Gross, 2009).…”