wm/aggregate-rivers.sql

50 lines
1.5 KiB
PL/PgSQL

/* Aggregates rivers by name and proximity. */
drop function if exists aggregate_rivers;
create function aggregate_rivers() returns table(
id bigint,
name text,
way geometry
) as $$
declare
c record;
cc record;
changed boolean;
begin
while (select count(1) from wm_rivers_tmp) > 0 loop
select * from wm_rivers_tmp limit 1 into c;
delete from wm_rivers_tmp a where a.id = c.id;
changed = true;
while changed loop
changed = false;
for cc in (
select * from wm_rivers_tmp a where
a.name = c.name and
st_dwithin(a.way, c.way, 500)
) loop
c.way = st_linemerge(st_union(c.way, cc.way));
delete from wm_rivers_tmp a where a.id = cc.id;
changed = true;
end loop;
end loop; -- while changed
return query select c.id, c.name, c.way;
end loop; -- count(1) from wm_rivers_tmp > 0
return;
end
$$ language plpgsql;
drop index if exists wm_rivers_tmp_id;
drop index if exists wm_rivers_tmp_gix;
drop table if exists wm_rivers_tmp;
create temporary table wm_rivers_tmp (id bigint, name text, way geometry);
create index wm_rivers_tmp_id on wm_rivers_tmp(id);
create index wm_rivers_tmp_gix on wm_rivers_tmp using gist(way) include(name);
insert into wm_rivers_tmp
select p.gid as id, p.vardas as name, p.geom as way from hidro_l p;
drop table if exists wm_rivers;
create table wm_rivers as (
select * from aggregate_rivers() where st_length(way) >= 50000
);
drop table wm_rivers_tmp;