IsoSurface depuis 1 point donné avec une tolérance donnée

CREATE OR REPLACE FUNCTION cncggetisosurface(geomdepart geometry,tolerance float,altitude double precision) 
RETURNS geometry AS 
$$
DECLARE
idcarredepart integer:=0;
carredepart geometry;
altituderef double precision:=0;

tempidgrid integer:=0;
tempgeom  geometry;
tempaltitude double precision:=0;
toutlageometrieavant geometry;
toutlageometrie geometry;
isendofstory boolean :=false;

BEGIN
    
    IF GeometryType(geomdepart) = 'POINT' THEN
 FOR tempidgrid,tempaltitude,tempgeom IN (SELECT idgrid_elevation,mns_lidar, the_geom FROM l3d_grid1m_elevation  
    WHERE ST_DWITHIN(the_geom,geomdepart, 0.01) 
  ) LOOP
  IF tempaltitude > altituderef THEN
   idcarredepart := tempidgrid;
   altituderef   := tempaltitude ;
   carredepart   := tempgeom;  
   
  
  END IF;
 END LOOP;
 --au depart etait le carre
 toutlageometrie := carredepart;  
    ELSE 
 --ensuite etait la geom carre,polygone etc...
 toutlageometrie := geomdepart; 
    END IF;
    
   
    WHILE NOT isendofstory LOOP
 toutlageometrieavant := toutlageometrie; 
 FOR tempaltitude,tempgeom IN (SELECT mns_lidar, the_geom FROM l3d_grid1m_elevation  
    WHERE ST_TOUCHES(the_geom,toutlageometrie) 
   ) LOOP
  IF abs(tempaltitude - altituderef)<=tolerance THEN  
   toutlageometrie := st_union(toutlageometrie, tempgeom);  
  END IF;
 END LOOP;
 IF ST_EQUALS(toutlageometrie,toutlageometrieavant) THEN
  isendofstory := true;
 ELSE
  toutlageometrie := cncggetisosurface(toutlageometrie ,tolerance,altituderef ); 
 END IF;
    END LOOP;

    RETURN toutlageometrie;
    
    
END;
$$ 
LANGUAGE plpgsql;

Et ensuite il suffit de tester avec un : SELECT st_astext(cncggetisosurface('SRID=21781;POINT(538608 153109)'::geometry,0.50,0.0));