CREATE OR REPLACE FUNCTION mk_the_geom() RETURNS trigger AS $mk_the_geom$

begin

if (new.the_geom is null) then
  new.the_geom = geomfromtext(\'POINT(\' || new.m_lon || \' \' || new.m_lat || \')\',-1);
end if;

return new;

end

$mk_the_geom$ LANGUAGE plpgsql;

CREATE TRIGGER mk_the_geom BEFORE INSERT ON multi_obs
    FOR EACH ROW EXECUTE PROCEDURE mk_the_geom();