CG_ConstrainedDelaunayTriangles — Return a constrained Delaunay triangulation around the given input geometry.
geometry CG_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.
        
                   
                      CG_ConstrainedDelaunayTriangles of 2 polygons 
 
                                        select CG_ConstrainedDelaunayTriangles(
                                        ST_Union(
                                        'POLYGON((175 150, 20 40, 50 60, 125 100, 175 150))'::geometry,
                                        ST_Buffer('POINT(110 170)'::geometry, 20)
                                        )
                                        );
                                    
                  
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                      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)
                                        )
                                        );
                                    
                  
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