Extrinsically smooth direction fields

Extrinsic - Zhiyang Huang (2016) ------------------------------------ This code implements the algorithm described in Huang Z, Ju T. Extrinsically smooth direction fields. Comput Graph(2016), http://dx.doi.org/10.1016/j.cag.2016.05.015i The basic function of this program is to compute extrinsically smooth direction fields “g” upon a curve, surface or volume while giving a references field “f”, such that “g” is orthogonal to “f”. In particular, the default setting of “f” for curve and surface are tangent field of the curve and normal field of the surface, respectively. The parameter-free initialization method based on least eigenvector problem and the Gauss–Seidel iterations, as described in the above paper, are implemented in this code and subjected to use. Currently the code is only tested on Mac OS X 10.10 or above, it should work at other platforms with minor modification.