lttb_3.sql

create aggregate largest_triangle (point_t,point_t,point_t) (
 stype = triangle_t,
 sfunc = largest_triangle_accum
);

create function largest_triangle_accum (maxsurfacetriangle triangle_t, p1 point_t, p2 point_t, p3 point_t)
returns triangle_t
language SQL
as $$
select
 case
   when maxsurfacetriangle is null or 
        triangle_surface(p1,p2,p3) > maxsurfacetriangle.surface
   then (p1,p2,p3,triangle_surface(p1,p2,p3))::triangle_t
  else maxsurfacetriangle
end
$$