D. W. Marquardt, “An Algorithm for Least-Squares Estimation of Nonlinear Parameters,” Journal of the Society for Industrial and Applied Mathematics, Vol. 11, No. 2, 1963, pp. 431-441. doi:10.1137/0111030
 A. D. Sappa and M. Rouhani, “Efficient Distance Estimation for Fitting Implicit Quadric Surfaces,” 16th IEEE International Conference on Image Processing ICIP, Cairo, 7-12 November 2009, pp. 3521-3524.
 X. Ying, L. Yang and H. Zha, “A Fast Algorithm for Multidimensional Ellipsoid-Specific Fitting by Minimizing a New Defined Vector Norm of Residuals Using Semidefinite Programming,” IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol.:1856-1863, 2012. doi:10.1109/TPAMI.2012.109
 S. W. Kwon, F. Bosche, C. Kim, C. T. Haas and K. A. Liapi, “Fitting Range Data to Primitives for Rapid Local 3D Modeling Using Sparse Range Point Clouds,” Automation in Construction, Vol. 13, No. 1, 2004, pp. 67-81. doi:10.1016/j.autcon.2003.08.007
 R. A. Calvo, M. Partridge and M. Jabri, “A Comparative Study of Principal Component Analysis Techniques,” Proceedings of Ninth Australian Conference on Neural Networks, Brisbane, 11-13 February 1998, pp. 276-281.
 L. Zhou and O. Salvado, “A Comparison Study of Ellipsoid Fitting for Pose Normalization of Hippocampal Shapes,” International Conference on Digital Image Computing Techniques and Applications (DICTA), Noosa, 6-8 December 2011. pp. 285-290.
 P. D. Simari and K. Singh, “Extraction and Remeshing of Ellipsoidal Representations from Mesh Data,” Proceedings of Graphics Interface, 9-11 May 2005, Canadian Human-Computer Communications Society, pp. 161-168.
 D. Marshall, G. Lukacs and R. Martin, “Robust Segmentation of Primitives from Range Data in the Presence of Geometric Degeneracy,” IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 23, No. 3, 2001, pp. 304-314. doi:10.1109/34.910883
 P. Morena at Thingiverse, “Treefrog STL Model,” 2012. http://www.thingiverse.com/download:61236
 E. Carlos at GrabCAD, “Fan STL Model,” 2012. http://grabcad.com/library/carcasa-de-un-ventilador-paraensayos/files/carca.stl