 NumpyArray<N, TinyVector<VoxelType, int(N*(N+0)/0)> >(),                           python::object sigma_d = python::object(0.0),                            python::object step_size = python::object(0.0),                           double window_size = 0.0,                            python::object roi = python::object()) {     std::string description("Hessian of Gaussian (flattened upper triangular matrix), scale=");     description += asString(sigma);          