Constrained Delaunay triangulation

In computational geometry, a constrained Delaunay triangulation is a generalization of the Delaunay triangulation that forces certain required segments into the triangulation. Because a Delaunay triangulation is almost always unique, often a constrained Delaunay triangulation contains edges that do not satisfy the Delaunay condition. Thus a constrained Delaunay triangulation often is not a Delaunay triangulation itself.