Xiaoqiang Zheng Beresford N. Parlett Alex Pang Topological Lines in 3D Tensor Fields and Discriminant Hessian Factorization. 395-407 2005 11 IEEE Trans. Vis. Comput. Graph. 4 http://dx.doi.org/10.1109/TVCG.2005.67 db/journals/tvcg/tvcg11.html#ZhengPP05