On -sets of class in

Let m , n be two positive integers, a subset K of points of the finite desarguesian 3-dimensional projective space PG ( 3 , q ) is of class [ 1 , m , n ] 2 if every plane of PG ( 3 , q ) intersects K either in 1, or m or n points. We shall present a result on ( q 2 + q + 1 ) -sets of points of PG ( 3 , q ) of class [ 1 , m , n ] 2 which implies a characterization of quadric cones of PG ( 3 , q ) , q odd.