“…These can be roughly divided into two categories: 2D view-based and 3D modelbased approaches. Examples of the former include the use of support vector machines (SVM) [16,22], PCA [32], Kernel PCA (KPCA) [8], independent subspace analysis [33], Gabor filters [41,42] and networks [19], active appearance models (AAM) [11], shape-from-shading [9] and 2D geometric heuristics [23], amongst others. Model-based approaches can be tackled from a concise mathematical formulation [15], or if real-time analysis is required, by simplifying the problem using affine transformations [13].…”