CREATE TYPE region_distance AS (boundary_gid integer, distance double precision);

CREATE OR REPLACE FUNCTION nt_compute_boundary_distances ( geometry ) RETURNS setof region_distance AS $$
DECLARE
BEGIN
    RETURN QUERY select Q.gid, sum(dist) from
        (select gid, length(transform(intersection(the_geom, $1),27500)) as dist
            from boundary_p_v2 where intersects(the_geom, $1) is true ) Q
                group by gid;
END;
$$
LANGUAGE 'plpgsql';