ST_ConstrainedDelaunayTriangles — Return a constrained Delaunay triangulation around the given input geometry.
geometry ST_ConstrainedDelaunayTriangles(geometry  g1);
Return a Constrained Delaunay triangulation around the vertices of the input geometry. Output is a TIN.
            
            This method needs SFCGAL backend.
        
Availability: 3.0.0
            
            This function supports 3d and will not drop the z-index.
        
![]() ST_ConstrainedDelaunayTriangles of 2 polygons 
 
select ST_ConstrainedDelaunayTriangles(
               ST_Union(
                       'POLYGON((175 150, 20 40, 50 60, 125 100, 175 150))'::geometry,
                       ST_Buffer('POINT(110 170)'::geometry, 20)
                   )
           );
				
  | ![]() ST_DelaunayTriangles of 2 polygons. Triangle edges cross polygon boundaries. 
 
select ST_DelaunayTriangles(
               ST_Union(
                       'POLYGON((175 150, 20 40, 50 60, 125 100, 175 150))'::geometry,
                       ST_Buffer('POINT(110 170)'::geometry, 20)
                   )
	   );
  |