One potential limitation or challenge in applying the Delaunay triangulation approach to constructing the transfer matrix for complex geometries is the computational cost and complexity of the triangulation process. In complex geometries with irregular boundaries or intricate shapes, the Delaunay triangulation may result in a large number of triangles or tetrahedra, leading to increased computational overhead. Additionally, ensuring the quality of the triangulation and the accuracy of the interpolation in regions with sharp features or high curvature can be challenging. The Delaunay triangulation approach may also struggle with handling concave geometries or regions with narrow passages, where the triangulation may not capture the geometry accurately.