Mesh holes formed by those boundaries for which no Dirichlet boundary conditions are given as suggest in Marchandise et al. (2014) Optimal parametrizations for surface remeshing. See Figure 9.
Use Vector3D<double> as voxel type to enable the caching of a 4D displacement field which is generated by a 4D transformation or a 3D SV FFD integrated over multiple time intervals.
Generalize implementation and extend FreeFormTransformation API such that this constraint can be used with any deformable transformation model. The current implementation is specific to the 3D cubic B-spline FFD.