ST_3DUnion — Perform 3D union
geometry ST_3DUnion(geometry geom1, geometry geom2);
Availability: 2.2.0
 This method needs SFCGAL backend.
 This function supports 3d and will not drop the z-index.
 This function supports Polyhedral surfaces.
 This function supports Triangles and Triangulated Irregular Network Surfaces (TIN).
3D images were generated using PostGIS ST_AsX3D and rendering in HTML using X3Dom HTML Javascript rendering library.
 SELECT ST_Extrude(ST_Buffer(ST_GeomFromText('POINT(100 90)'),
 50, 'quad_segs=2'),0,0,30) AS geom1,
        ST_Extrude(ST_Buffer(ST_GeomFromText('POINT(80 80)'),
 50, 'quad_segs=1'),0,0,30) AS geom2;
                
 ![]() Original 3D geometries overlaid. geom2 is the one with transparency.  | 
 SELECT ST_3DUnion(geom1,geom2)
FROM ( SELECT ST_Extrude(ST_Buffer(ST_GeomFromText('POINT(100 90)'),
 50, 'quad_segs=2'),0,0,30) AS geom1,
        ST_Extrude(ST_Buffer(ST_GeomFromText('POINT(80 80)'),
 50, 'quad_segs=1'),0,0,30) AS geom2 ) As t;
 ![]() Union of geom1 and geom2  |