wm/aggregate-rivers.sql

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